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Persistent changes of electrical properties of CdTe/CdMgTe heterostructures induced by multiple cooling-heating temperature cycles and hydrostatic pressure
Abstract
We have shown that multiple cooling-heating temperature cycles and the
application of external pressure led to persistent changes of the sheet
electron density and the mobility in low dimensional CdTe/CdMgTe quantum
structures grown on GaAs substrates. This process was of minor
importance if a difference between the relative variation of the lattice
constant of the II-VI material and the GaAs substrate induced by
external fields (hydrostatic pressure and temperature) was smaller than
about 0.06%.
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In this article lasing action of (CdMg)Te quantum well laser structures is reported. The separate confinement quantum well laser structures were grown by molecular beam epitaxy. Stimulated emission has been observed at 77 K and at room temperature. The structures emitted at wavelengths of around 650 nm at room temperature. A (CdMg)Te/CdTe superlattice has been used for the active layer as well as for the electrical confinement layer. Due to this an efficient radiative recombination even at room temperature could be obtained. The distribution of the intensity of the light across the waveguide has been calculated.
We have found that in modulation-doped CdTe/Cd1—xMgxTe : I heterostructures a non-intentional formation of a potential valley outside the quantum well in the region doped with iodine donors is the origin of parallel transport. We have shown the rules how to choose the parameters of the quantum structure in order to eliminate this phenomenon. Electrical measurements performed on specially designed samples, which had parameters of the quantum structure fulfilling the mentioned rules, showed the formation of two-dimensional electron gas without parallel electron transport.
We have shown how various parasitic phenomena can influence electrical properties of low dimensional CdTe/Cd1−xMgxTe heterostructures, and how they can be minimized or even eliminated. We have found that: (1) a parallel conduction caused by spontaneous formation of a potential valley in the region of the doping with iodine donors is eliminated if a spacer separating QW from the doping region is not thicker than 20 nm and the quantum well depth is greater than about 240 meV; (2) the cap layer at least 150 nm wide protects free electrons in the quantum well and/or the doping layer from trapping by surface defects; (3) the use of thick buffer layer between the substrate and the structure leads to a significant improvement of the sample stability under hydrostatic pressure making a degradation process, observed even without pressure, much less essential than in samples with thin buffer layers. © 2002 American Institute of Physics.
II–VI ZnSe (binary) and ZnSSe (ternary) widegap compound semiconductor based photovoltaic devices (p–i–n and avalanche photodiodes (APDs)) are developed for the blue–violet (460–400 nm) optical wavelength region by molecular beam epitaxial (MBE) growth. The ternary compound ZnSSe p–i–n structure photodiodes, grown with complete lattice matched condition on GaAs substrates, exhibit high external quantum efficiencies of 80–70% in the blue-violet optical region with extremely low dark currents (∼pA/mm2), These diodes reveal stable and long-lived operation at 300 K. Also presented is ZnSe and ZnSSe based blue–violet APD devices, fabricated by precise defect control and process techniques. This new device has revealed large signal gain (G) of G = 50 for ZnSe, and G = 60 for the ZnSSe APD device under high electric field strength of (0.8–1.1) × 106 V/cm. Important device parameters, ionization coefficients of photo-injected electrons and holes, and device stability are also discussed.
Numerical Data and Functional Relationships in: Science and Technology edited by O
- Landolt-Börnstein