Hans Zogg

ETH Zurich | ETH Zürich · Department of Physics

Mid-infrared Vertical External Cavity Surface Emitting Lasers (VECSEL) based on narrow gap lead-chalcogenide (IV-VI) semiconductors exhibit strongly reduced threshold powers if the active layers are structured laterally for improved optical confinement. This is predicted by 3-d optical calculations; they show that lateral optical confinement is nee...

We present continuously tunable Vertical External Cavity Surface Emitting Lasers (VECSEL) in the mid-infrared. The structure based on IV–VI semiconductors is epitaxially grown on a Si-substrates. The VECSEL emit one single mode, which is mode hop-free tunable over 50–100 nm around the center wavelength. In this work, two different devices are prese...

It is explained with a simple model why the reduction of threading dislocation (TD) densities in epitaxial lattice and thermal expansion mismatched IV–VI layers such as PbSe(111) on Si(111) substrates follows a 1/h 2 dependence where h is the thickness of the layer. This is in contrast to the 1/h dependence for III–V and II–VI layers grown on misma...

Optically pumped VECSEL (vertical external cavity surface emitting lasers) based on IV-VI semiconductors grown on Si cover the entire wavelength range between 3.0 and 10 μm. Thanks to their simple structure and large wavelength coverage they are an interesting alternative laser technology to access the mid-infrared wavelength region. The active lay...

Continuously tunable Vertical External Cavity Surface Emitting Lasers (VECSEL) have been realized, emitting in the 3-5 µm range. Pulsed output power at room temperature operation is > 10 mWp, in the single Gaussian TEM00 emission mode.

Vertical external cavity surface emitting lasers in the wavelength region from 3–5 μm are presented. They are based on PbSe quantum wells grown on Si substrates. As host material Pb 1‐ x Eu x Se and Pb 1‐ x Sr x Se are used. With Pb 1‐ x Sr x Se as host material maximum operation temperatures of 325 K are achieved, while with...

In this work investigations of sputtering of monocrystalline (1 1 1)-oriented epitaxial films of semiconductor ternary solid solutions of Pb(1-x)Sn(x)Te (x = 0.00-0.56), Pb(1-x)Eu(x)Te (x = 0.00-0.05), Pb(1-x)Sn(x)Se (x = 0.00-0.07), Pb(1-x)Eu(x)Se (x = 0.00-0.16, x = 1.00), Pb(1-x)Sn(x)S (x = 0.00-0.05) on Si(1 1 1) and BaF(2)(1 1 1) substrates in...

High efficiency laser operation with output power exceeding 2 W was obtained for vertical external-cavity PbS based IV-VI compound surface emitting quantum-well structures. The laser showed external quantum efficiency as high as 16%. Generally, mid-infrared III-V or II-VI semiconductor laser operation utilizing interband electron transitions are re...

A singlemode tunable vertical external cavity surface emitting laser (VECSEL) has been realised. The VECSEL can be tuned continuously over more than 80 nm from ~3.22 to 3.3μm wavelength. Tuning is performed by changing the cavity length with a piezoelectric driver. Covering this wavelength range allows various potential applications, especially for...

A mid-infrared vertical external cavity surface emitting laser (VECSEL) based on undoped PbS is described herein. A 200 nm-thick PbS active layer embedded between PbSrS cladding layers forms a double heterostructure. The layers are grown on a lattice and thermal expansion mismatched Si-substrate. The substrate is placed onto a flat bottom Bragg mir...

This chapter is devoted to IV-VI materials, especially their growth and application as infrared sensors and infrared laser diodes for wavelengths ranging from about 3 gm to above 14 gm.

Single mode continuously tunable mid-infrared Vertical External Cavity Surface Emitting Lasers (VECSEL) have been realized. Emission wavelength is ~5 microns with a tuning range >100 nm. Output power at room temperature is >10 mWp.

Mid-infrared vertical external cavity surface emitting lasers based on PbSe/PbSrSe multi-quantum-well structures on Si-substrates are realized. A modular design allows growing the active region and the bottom Bragg mirror on two different Si-substrates, thus facilitating comparison between different structures. Lasing is observed from 3.3 to 5.1 mu...

Porous structures of lead chalcogenides with porosities of 20-68% and pore dimensions as small as 7-20 nm were fabricated using an anodic electrochemical etching technique applied to epitaxial PbTe and PbSe films on Si. Anodized lead selenide demonstrated two basic types of porous morphology: quasiporous noncontinuous layers and hierarchical porous...

CdTe/CdS solar cells of —10% efficiency, developed with a vacuum deposition method were irradiated with high-energy protons of different fluences. The V oc and f.f. of irradiated cells increase or decrease depending on the fluence. The normal soda lime glass substrate darkens under the irradiation; therefore low Isc is measured. Measurements sugges...

We review MBE growth of epitaxial IV-VI layers on Si(111) substrates and fabrication of photovoltaic infrared devices in the layers. Cut-off wavelengths are chemically tailored from 3 µm up to above 12 µm by using PbS, PbTe, Pb1−xEuxSe and Pb1−xSnxSe. An intermediate epitaxial stacked CaF2-BaF2 bilayer of 200 nm thickness serves to overcome the lar...

Heteroepitaxial films of (111)BaF2/CaF2 on (111)silicon, and (111)BaF2 on (100)silicon are used as substrates for the growth of IV-VI semiconductors. X-ray diffraction measurements show that p-type PbSxSe1-x(0.4 < × < 0.5) films grown on BaF2/CaF2/Si(111) substrates have bi-crystalline (111) and (100) characteristics. This, combined with thermal st...

Narrow-gap PbSe and PbSe1−xTex films were grown by MBE on 3n-Si(111) wafers. The layers are used for IR-sensor array applications. Epitaxy was achieved by using an intermediate CaF2/BaF2 bilayer to overcome the large difference in lattice constants (14%) and thermal expansion coefficients (700%). While PbSe is rather soft, the hardness increases wi...

The strain induced by the thermal mismatch in Pbl−xSnxSe and other IV–VI compound layers on Si(111)-substrates relaxes by glide of dislocations in the main <110> {001}-glide system. The glide planes are arranged with 3-fold symmetry and inclined to the (111)-surface. Despite a high threading dislocation density (> 107 cm−2) in these heavily lattice...

Epitaxial CdTe has been grown onto Si(lll) wafers by MBE with the aid of a composition graded (Ca,Ba)F2 buffer layer to surmount the large misfit of 19%. Untwinned CdTe layers with smooth surfaces, narrow X-ray lines and strong photoluminescence with a narrow near band edge peak were obtained. The results indicate a comparable structural quality to...

We report on PbSe QDs grown on a few μm thick PbTe(111) layers on Si(111). The QDs form as pyramids with three (100) side faces and (111) base. Their sizes are almost equal, the standard deviation of their heights can be as low as 2-3%. This seems to be the narrowest distribution ever observed for self assembled QDs. Similar QDs of PbSe have first...

Narrow gap IV-VI materials like PbS, PbSnSe and PbSnTe are used for infrared detector device fabrication [1,2]. Earlier an intermediate Ila-fluoride buffer layer, which consisted of a BaF2/CaF2-stack of about 2000 Å thickness, was used to get epitaxial high quality layers on silicon substrates. This buffer is now reduced to a much thinner layer of...

Low substrate temperatures have to be used for polymer substrates. Therefore, using soda- lime glass (SLG) substrates with and without an alkali barrier (Al2O3), a three-step CIGS coevaporation process for a substrate temperature of 450 °C has been developed and compared to film deposition with constant evaporation rates. The three-step process was...

We present new results on structural and electronic properties of epitaxial lead chalcogenides on Si-substrates. A stacked MBE-grown CaF 2 /BaF 2 buffer of 200 nm thickness serves to overcome the large lattice- and thermal expansion mismatches. Lead chalcogenide layers are grown by MBE or HWE with thicknesses of a few μm. The X-ray rocking curve wi...

Graded (Ca,Ba)F//2 layers consisting of near lattice matched CaF//2 at the Si interface and of BaF//2 with 14% increased lattice constant at the top surface were grown by molecular beam epitaxy (MBE) on Si(111). Smooth and crackfree layers exhibiting Rutherford backscattering (RBS) channeling minima below 5% were obtained. Device quality epitaxial...

A tunable PbTe based mid-infrared vertical external cavity surface emitting laser is described. The active part is a ∼ 1 μm thick PbTe layer grown epitaxially on a Bragg mirror on the Si-substrate. The cavity is terminated with a curved Si/SiO Bragg top mirror and pumped optically with a 1.55 μm laser. Cavity length is <100 μm in order that only on...

Wavelength tunable emitters and detectors in the mid-IR wavelength region allow applications including thermal imaging and gas spectroscopy. One way to realize such tunable devices is by using a resonant cavity. By mechanically changing the cavity length with MEMS mirror techniques, the wavelengths may be tuned over a considerable range. Resonant...

Mid-IR tunable VECSELs (Vertical External-Cavity Surface-Emitting Lasers) emitting at 4–7 μm wavelengths and suitable for spectroscopic sensing applications are described. They are realized with lead-chalcogenide (IV–VI) narrow band gap materials. The active part, a single 0.6–2-μm thick PbTe or PbSe gain layer, is grown onto an epitaxial Bragg mir...

The SnTe, Sn _{1- x} Eu _x Te and Sn _{1- x} Sr _x Te ( x <0.06) films were prepared by hot wall epitaxy. The ternary alloy films prepared in cation rich condition had hole concentration around 1×10¹⁹ cm ^-3 with high mobility exceeding 2000 cm ²/ V   s at room temperature. O...

Mid-infrared vertical external cavity surface emitting lasers (VECSEL) were developed for the wavelength range 4 to 5 μm. The devices are based on lead salt materials grown by MBE on BaF2 or Si substrate. The VECSELs are optically pumped with a 1.55 μm wavelength laser. They are operating up to above room temperature. An output power 6 mWp was reac...

We describe a tunable resonant cavity enhanced detector (RCED) for the mid-infrared employing narrow gap lead-chalcogenide (IV–VI) layers on a Si substrate. The device consists of an epitaxial Bragg reflector layer, a thin p–n+ heterojunction with PbSrTe as detecting layer and a micro-electro-mechanical system (MEMS) micromirror as second mirror. D...

We describe the growth and formation of self assembled PbTe quantum dots in a CdTe host on a silicon (111) substrate. Annealing yields different photoluminescence spectra depending on initial PbTe layer thickness, thickness of the CdTe cap layer and annealing temperature. Generally two distinct emission peaks at ∼0.3 eV and ∼0.45 eV are visible. Mo...

Mid-infrared vertical external cavity surface emitting lasers (VECSELs) emitting above 1 W output power in pulsed mode and up to 17 mW in continuous mode at −172 °C were realized. Emission wavelength changes from 5 μm at −172 °C to 3.6 μm at 20 °C heat sink temperature. The active medium is a one wavelength thick PbTe layer grown by molecular beam...

The authors describe the first mid-infrared VECSELs (vertical external cavity surface emitting laser) operating up to above room temperature. They employ a resonant design with a one wavelength optical thickness of the active layer (PbSe or PbTe). The structures are grown non-lattice matched on BaF2 or Si substrate by solid state molecular beam epi...

Comprehensive research of the structural, optical and electrical properties of a PbTe/CaF2/Si(1 1 1) epitaxial system after anodic electrochemical treatment in a Norr solution electrolyte with a low current density of 6 mA cm−2 was carried out. It is shown that the anodizing results in the increase of the band gap and resistivity and in the decreas...

Wavelength tunable emitters and detectors in the mid-IR wavelength region allow applications including thermal imaging and spectroscopy. Such devices may be realized using a resonant cavity. By mechanically changing the cavity length with MEMS mirror techniques, the wavelengths may be tuned over a considerable range. Vertical external cavity surfac...

The surface modification of lead chalcogenide epitaxial films during plasma treatment processes is investigated. With AFM and SIMS measurements it was shown that the mechanism of a microhillock formation is the micromasking effect of dislocation exit sites. Micromasking, and hence microhillock formation, takes place when fluorine sputtered from rea...

A midinfrared vertical external cavity surface emitting laser with 4.5 μm emission wavelength and operating above room temperature has been realized. The active part consists of a single 850 nm thick epitaxial PbSe gain layer. It is followed by a 2 1/2 pair Pb1−yEuyTe/BaF2 Bragg mirror. No microstructural processing is needed. Excitation is done op...

The realization of a vertically moving micromirror using electrostatic actuation in a comb drive configuration is presented. The micromirror is designed for the use in tunable mid-infrared Resonant Cavity Enhanced Detectors (RCEDs). It can be displaced more than 2.5μm with less than 30V actuation voltage. In addition to the pure out-of-plane moveme...

CuIn1 − xGaxSe2 (CIGS) solar cells show a good spectral response in a wide range of the solar spectrum and the bandgap of CIGS can be adjusted from 1.0 eV to 1.7 eV by increasing the gallium-to-indium ratio of the absorber. While the bandgaps of Ga-rich CIGS or CGS devices make them suitable for top or intermediate cells, the In rich CIGS or CIS de...

Optically pumped VECSELs (vertical external cavity surface emitting lasers) with above 5 mum emission wavelength were fabricated on BaF2 and Si substrates. The active layer is just 1 - 2 mum thick PbTe or PbSe, and epitaxial PbEuTe/BaF2 or PbSrTe/EuTe Bragg mirrors are employed. On BaF2 substrates, output powers up to 260 mW pulsed and 3 mW cw at 1...

A mid-infrared vertical external cavity surface emitting laser (VECSEL) on a Si substrate has been realised. It is optically pumped and emits around 5 mum wavelength. Maximum output power of 26 mW_p (limited by the 1.5 m wavelength pump laser) was observed at 100 K operating temperature with 3 s pulse widths. The active part is just a 1.3...

Mid-infrared vertical external cavity surface emitting lasers (VECSELs) for 5 microm in wavelength have been realized. The active parts are of a simple structure, either a 2 microm thick PbTe gain layer or two 150 nm PbTe layers embedded in Pb(1-x)Eu(x)Te barriers. Epitaxial 2.5 pair Pb(1-y)Eu(y)Te/BaF(2) Bragg mirrors are employed to form the cavi...

Results on a tunable resonant cavity enhanced detector (RCED) in the mid-infrared employing a vertically moving, comb-drive actuated micromirror are presented. A wide tuning range of 0.7 mum and a low order configuration have been achieved with a micromirror displacement range of 2.5 mum and a reduction of the optical cavity length respectively.

Lead chalcogenide (IV–VI narrow-gap semiconductor) layers on Si or BaF2(111) substrates are employed to realize two mid-infrared optoelectronic devices for the first time. A tunable resonant cavity enhanced detector is realized by employing a movable mirror. Tuning is across the 4μm to 5.5μm wavelength range, and linewidth is <0.1μm. Due to the thi...

Mid-infrared detectors that are sensitive only in a tunable narrow spectral band are presented. They are based on the Resonant Cavity Enhanced Detector (RCED) principle and employing a thin active region using IV-VI narrow gap semiconductor layers. A Fabry-Pérot cavity is formed by two mirrors. The active layer is grown onto one mirror, while th...

We describe two new optoelectronic mid-IR devices employing narrow gap lead-chalcogenide (IV-VI) layers on Si or BaF2 substrates: (1) Tunable resonant cavity enhanced detectors (RCED) for the mid-infrared with an epitaxial Bragg mirror and a thin p-n+ heterojunction as detecting layer have been realized for the first time. They are tunable by movin...

Two types of radiative transitions were observed in the low-temperature photoluminescence spectra of Pb1−x Eux Te (0 ≤ x ≤ 0.09) solid solutions: an intense line corresponding to the transitions from the conduction to the valence band and a series (up to 15) of narrow lines corresponding to the transitions from the hybridized conduction band to the...

This paper presents continuative results on the design, fabrication and measurements of a vertically moving, electrostatically actuated micromirror, first shown at the IEEE MEMS 2007 [N. Quack, I. Züst, S. Blunier, J. Dual, M. Arnold, F. Felder, M. Rahim, H. Zogg, Electrostatically actuated micromirror for resonant cavity enhanced detectors, 20th I...

Highly sensitive photodetectors for the mid-infrared have recently been obtained by placing a photodiode inside a Fabry–Pérot cavity (Arnold et al 2005 Appl. Phys. Lett. 87 141103). These resonant cavity enhanced detectors (RCED) are sensitive at the resonances which depend on the distance between the two mirrors of the cavity (Unlu and Strite 1995...

Tunable resonant cavity enhanced detectors (RCED) have been realised for the mid-infrared (IR). The bottom mirror as well as the photodiode inside the cavity are based on narrow gap IV–VI materials and grown by molecular beam epitaxy (MBE) on Silicon substrate. The length of the cavity and therefore the resonance wavelengths can be adjusted continu...

We present the first mid-infrared VECSEL (Vertical External Cavity Surface Emitting Laser) for wavelengths above 3 μm. The structure is very simple: A 2 μm thick PbTe layer is embedded between two high reflectance mirrors and used as gain medium. It is optically pumped with a 1.5 μm wavelength laser. Emission is around 5 μm wavelength and output po...

X-ray, Auger-electron spectroscopy, scanning electron microscopy and atomic force microscopy investigations of the Pb1−xEuxSe film structure with variation of x from 0.00 to 0.16 were carried out. The 2–4 µm thick films were grown on Si (1 1 1) substrates with a CaF2 buffer layer by molecular beam epitaxy. We show that the films have a high structu...

Midinfrared vertical external cavity surface emitting lasers for 5 μm wavelength have been realized. The active parts consist either of a 2 μm thick PbTe gain layer or of two 150 nm PbTe layers embedded in Pb1−xEuxTe barriers, and an epitaxial two pair Pb1−yEuyTe/BaF2 Bragg mirror. They are optically pumped with a 1.5 μm laser. No precautions for e...

Midinfrared tunable resonant cavity enhanced detectors have been realized. The linewidths of 0.07 μ m are determined by the finesse of the cavities, while the length of the cavity can be changed with a movable mirror. This allows tuning across the 4–5.5 μ m midinfrared wavelength range. The thin (0.3 μ m ) photodiodes inside the cavity are based on...

CdTe polycrystalline thin film solar cells have a strong potential in scalability. They have shown long-term stable performance and high efficiency up to 16.5% under AM1.5 illumination. Amongst several attractive features high chemical stability of CdTe and a simple compound formation are the most important ones for large area production of solar m...

We present a different back contact for CdTe solar cell by the application of only a transparent conducting oxide (TCO), typically ITO, as a back electrical contact on all-PVD CdTe/CdS photovoltaic devices that acts as a free-Cu stable back contact and at the same time allows to realize bifacial CdTe solar cells, which can be illuminated from eithe...

Highly sensitive photodetectors for the mid infrared have been obtained by placing a photodiode inside a Fabry Perot cavity. These resonant cavity enhanced detectors (RCED) are sensitive at the resonances only, which depend on the distance between the two mirrors of the cavity. Displacing one of these mirrors allows changing the cavity length and t...

Epitaxial n-PbTe films grown on CaF2/Si(1 1 1) wafers using MBE were treated in an inductively coupled high-density Ar-plasma for a time period of 30 s. AFM measurements showed that after the treatment process large hillocks, 350–450 nm high, are formed on the dislocation exit sites. The tips of the hillocks have triangular dislocation exit pits. T...

Cu(In,Ga)Se2 (CIGS) solar cells on aluminum foils offer the advantage to be flexible, lightweight and, because of the low cost substrate, can be used for several applications, especially in buildings, where aluminum is already commonly used. There are reports of a-Si solar cells on Al foil, but to our knowledge development of CIGS solar cells on Al...

This paper presents the design, fabrication and measurement results of a vertically moving, electrostatically actuated micromirror. The single crystalline silicon substrate allows the design of a symmetrical and mechanically stable mirror suspension while keeping a geometry with high fill factors and maintaining elasticity and thus keeping the actu...

This paper analyses the photovoltaic parameters of the most promising CdS/CdTe solar cells for large application prepared by close space sublimation (CSS) and high vacuum evaporation (HVE). CdS/CdTe solar cells that have an efficiency of~10 % have been studied by current-voltage, capacitance-voltage and quantum efficiency measurements. The current-...

Development of flexible and lightweight solar cells is interesting for terrestrial and space applications that require a very high specific power (kW/kg) and flexibility for curved shaping or rolling. Flexible CdTe/CdS solar cells of 11% efficiency in superstrate and 7.3% efficiency in substrate configurations have been developed with a “lift-off”...

Recent developments in the technology of high vacuum evaporated CdTe solar cells are reviewed. High-efficiency solar cells of efficiencies up to 12.5% have been developed on soda-lime glass substrates with a low-temperature (<450 °C) process. This simple process is suitable for in-line production of large-area solar modules on glass as well as on f...

Narrow spectral band infrared detectors are required for multispectral infrared imaging. We review the first photovoltaic resonant cavity enhanced detectors (RCED) for the mid-IR range. The lead-chalcogenide (PbEuSe) photodetector is placed as a very thin layer inside an optical cavity. At least one side is terminated with an epitaxial Bragg mirror...

Narrow spectral band infrared detectors are required for multispectral infrared imaging. Wavelength selectivity can be obtained by placing passive line filters in front of the detectors, or, the preferred choice, by making the detectors themselves wavelength selective. We review the first photovoltaic resonant cavity enhanced detectors (RCED) for t...

Narrow gap IV-VI (lead chalcogenide) compounds are employed since long time as mid-IR-detectors and -lasers. IV-VIs are tolerant to structural defects (dislocations). This allows lattice mismatched MBE-growth on foreign substrates like Si which offers significant advantages with respect to size, costs and thermal conductivities. In addition,...

A simple approach for the analysis of mosaic epitaxial layers is proposed, based on a Patterson-like analysis of the reciprocal-space distribution of the scattered intensity. Within this approach, the mosaic-block-shape function P and the deformation correlation function are determined. The method is used for the analysis of relaxed PbTe epitaxial...

High-efficiency resonant-cavity-enhanced photodetectors for the mid-wavelength infrared range have been realized. Spectral linewidths as narrow as 0.07 μ m at 4.13 μ m and 0.24 μ m at 8.41 μ m center wavelength, respectively, have been achieved. Peak quantum efficiencies are up to above 50%. The photovoltaic devices are based on IV-VI semiconductor...

Incorporation of sodium into Cu(In,Ga)Se2 (CIGS) absorber layers and low-temperature absorber growth processes are important issues for the processing of flexible CIGS solar cells, particularly when polymer substrates are used. Na present during growth of CIGS is known to influence the growth kinetics and to lead to structurally and electronically...

A simple process for the deposition of Cu(In,Ga)Se2 (CIGS) absorber layers is described. A low-cost CIGS precursor paste deposited by simple and fast doctor blade technique is subsequently selenized under selenium vapour in a quartz tube at 10 mbar (10 min at 550 °C). The precursor paste is prepared with metal chlorides and nitrates dissolved in al...

A resonant cavity enhanced detector (RCED) sensitive at 4.4μm wavelength has been realized with lead–chalcogenide narrow band gap materials grown on a Si(111) substrate. It consists of a resonant cavity containing the thin Pb1-yEuySe infrared detector and a Pb1-xEuxSe(x>y) spacer layer. The bottom Bragg mirror is formed by 2 pairs of λ/4Pb1-xEuxSe/...

Incorporation of a small amount of sodium into Cu(In,Ga)Se2 (CIGS) absorbers for thin-film solar cells is well known to enhance conversion efficiencies. Usually, Na is added in a way such that it is present during CIGS growth and therewith influences the growth kinetics. We have used post-deposition Na in-diffusion into as-grown, Na-free absorbers...

Development of Cu(In,Ga)Se₂ (called CIGS) solar cells on polymers is challenging because of the thermo-physical properties of layers and substrates. CIGS layers of suitable structural and opto-electronic properties should be grown at low temperature (< 500°C) as polyimides tend to degrade at higher deposition temperatures. Additionally,...

Two types of novel lead-chalcogenide mid-IR emitters grown by molecular beam epitaxy (MBE) on Si or BaF(2) substrates are described:PbSe/PbEuSe edge emitting double heterostructure (DH) and quantum well (QW) lasers are pumped optically with low-cost III-V laser-diodes. They emit in the 3-6 microm range with powers up to 200 mW. Tuning is performed...

Two low cost infrared sources emitting above 4 μm wavelength are described: (i) An epitaxial EuSe/PbSe/Pb1−xEuxSe active resonant cavity with integrated top and bottom mirror on a Si(111) substrate transforms the incoming 0.9 μm pump radiation to e.g. 4.2 μm wavelength. The device operates at room temperature, and the width and value of the emissio...

Nano-particulate copper and indium metal layers of 1–2 μm have been deposited by non-vacuum techniques such as doctor blade, screen printing and electrospray using alcoholic suspension pastes. Electrospray showed a high efficiency of material usage and yielded the most uniform morphology. The metal precursor layers were subjected to a thermal treat...

The stability of CdTe/CdS solar cells depends on spatial changes of defects and impurities throughout the cell. Degradation effects are often associated with metal diffusion from the back contact of the cell, which is Cu in most cases. However, cells with stable back contact can also exhibit instability, as also all the other cell layers are potent...

Cu(In,Ga)Se ₂ (CIGS) absorber layers for thin-film solar cells were grown without sodium. Na was diffused into some of the absorbers after growth, which led to strongly improved device performance compared with Na-free cells. Efficiencies of 13.3% and 14.4% were achieved at substrate temperatures as low as 400 and 450 ° C , respectively....

Polycrystalline thin-film CdTe/CdS solar cells have been developed in a configuration in which a transparent conducting layer of indium tin oxide (ITO) has been used for the first time as a back electrical contact on p-CdTe. Solar cells of 7·9% efficiency were developed on SnOx:F-coated glass substrates with a low-temperature (<450°C) high-vacuum e...

Double heterostructure (DH) and quantum well (QW) EuSe/PbSe/Pb1−xEuxSe edge-emitting laser structures on Si substrates are grown by molecular-beam epitaxy. They operate up to 250 K when pumped with 870 nm low-cost laser diodes with peak powers of ∼7 W, and emit up to 200 mW peak output power at ∼5 μm wavelength. Differential quantum efficiencies ar...

A complete 2-d narrow gap infrared focal plane array on a Si-substrate where the Si-substrate contains the active addressing electronics was realized. Narrow gap IV–VI (lead chalcogenides like PbTe) layers grown epitaxially on Si(111)–substrates by molecular beam epitaxy serve as infrared sensitive detectors. The array consists of 96×128 pixels wit...

Two types of infrared emitters realised with IV-VI (lead chalcogenide) narrow-gap semiconductor materials on Si substrates are described. First, edge-emitting PbSe quantum well lasers with Pb_1-xEu_x Se claddings are grown on a BaF₂ buffer layer on Si[100] substrates, removed from the substrate by dissolving the buffe...

The electrical properties of heterojunctions between wide gap n-type oxides and the p-type semiconductor Cu(In,Ga)Se/sub 2/ have been studied. The investigated oxides were a bilayer of undoped and aluminium doped ZnO, and the commercially available transparent conducting oxides SnO/sub 2/:F (FTO) and In/sub 2/O/sub 3/-SnO/sub 2/ (ITO). The junction...

We have grown CuInSe/sub 2/ (CIS) and CuGaSe/sub 2/ (CGS) thin films with the 3-stage process in the presence and absence of Na and observed a Na-induced decrease of grain size for CGS, but not for CIS. In addition, sodium was found to hinder the interdiffusion of In and Ga in Cu(In,Ga)Se/sub 2/ (ClGS) layers, which has consequences for the achieve...

Precursor pastes for Cu(In,Ga)Se₂ (CIGS) were deposited by a simple and low cost deposition method. Selenization is performed using non-toxic roots to convert the precursor into a ClGS layer. Scanning electron microscopy and energy dispersive X-ray spectroscopy show homogenous films in composition, thickness and morphology, comparable to...

Cu(In,Ga)Se2 superstrate solar cells with efficiencies of up to 11.2% have been developed. Sodium which is considered beneficial for superstrate solar cells, has not been added to the cells presented in this contribution. The open circuit voltage and fill factor of as-deposited cells increase when light soaked under an illumination of one sun. A la...

Advances in nanoparticle technology led to powerful low-cost thin film techniques. Together with the established selenization method, these techniques open new possibilities for low-cost solar cell production that does not require expensive vacuum deposition systems. The chemical conversion (selenization) of nanosized precursor materials into CuInS...

Cu(In,Ga)Se2 (CIGS) layers have been deposited using the three-stage process on Mo coated soda-lime glass substrates with an alkali diffusion barrier. Sodium has been incorporated in such layers by NaF coevaporation, by deposition of NaF precursor layers and by diffusion of Na from a glass substrate without barrier. Scanning electron microscope pic...

The performance stability of CdTe/CdS solar cells is strongly determined by diffusion of impurities from the back contact into the absorber layer and hetero-junction. Impurity migration changes the effective carrier concentration and barriers in the device by compensation of donors or acceptors and by creation of defect centres. The CdS window laye...

Self-assembled PbSe quantum dots on PbTe quasisubstrates, where the quasisubstrate layer is grown on Si(111), show a size distribution as low as 2%, below any other reported size distribution. The result is explained by nonoverlapping diffusion radii for most of the dots and their nucleation occurring mainly at defects (glide steps of the quasisubs...

A two-dimensional narrow-gap infrared (IR) focal plane array on an Si substrate where the Si substrate contains the active addressing electronics is described. The array consists of 96 × 128 pixels with 75-μm pitch and is fabricated in a lead-chalcogenide layer grown epitaxially on the Si read-out chip. The cut-off wavelength is 5.5 μm. Each pixel...

Bak90 Times Cited:2 Cited References Count:11 , Bak90 Times Cited:2 Cited References Count:11 , Bak90 Times Cited:3 Cited References Count:11 , The following values have no corresponding Zotero field: Author Address: Rudmann, D Swiss Fed Inst Technol, ETH, Solid State Phys Lab, Thin Film Phys Grp, Technopk, CH-8005 Zurich, Switzerland Swiss Fed I...

Cu(In, Ga)Se 2 (CIGS) layers were grown with different vacuum evaporation recipes and the effects of sodium on the grain growth were investigated by scanning electron microscopy. A reduced grain size mainly in the lower part of films grown with the 3-stage process was observed when Na was available during growth. The growth kinetics were found to b...

Narrow gap IV-VI layers grown epitaxially on Si(111)-substrates by molecular beam epitaxy exhibit high quality despite the large lattice and thermal expansion mismatch. We present the further development of the first realization of a 2-d narrow gap IR-FPA an a Si-substrate containing the active addressing electronics: A 96 × 128 array with 75μm pit...

Polycrystalline thin film solar cells of II-VI compound semiconductors are important because of their low cost, high efficiency and stable performance. Flexible and lightweight solar cells are interesting for a variety of terrestrial and space applications that require a very high specific power (ratio of output electrical power to the solar module...