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Schematic cross-section of the GaN p-n junction diodes. a) Baseline GaN p-n diode and b) p-n diode with inserted InGaN layer to facilitate hole injection.
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GaN p‐n junction diodes grown on native GaN substrates have been fabricated and characterized. The devices exhibit a positive temperature coefficient of breakdown obtained from variable‐temperature current‐voltage measurements, confirming impact ionization avalanche. The low frequency noise characteristics of these devices have been measured under...
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... addition, the ratio of the impact ionization coefficients (α/β) is obtained from multiplication noise measurements and compared with results obtained from photocurrent-method extraction of the impact ionization coefficients. [5] 2. Device Structure and Fabrication Process Figure 1 shows a schematic cross-section of the device structures. Figure 1a shows the baseline GaN p-n diode. ...
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... 2. Device Structure and Fabrication Process Figure 1 shows a schematic cross-section of the device structures. Figure 1a shows the baseline GaN p-n diode. Grown on 2-in. ...
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... GaN substrates by metal-organic chemical vapor deposition, the structure (from top to bottom) consists of a 10 nm p þþ contact layer, a 100 nm p-GaN layer (Mg: 2Â10 19 cm À3 ), a 250 nm n-GaN drift layer (Si: 2Â10 16 cm À3 ), and 2 μm n þ -GaN layer (Si: 4Â10 18 cm À3 ). Figure 1b shows the GaN p-n diode structure with an InGaN layer used for hole injection in the excess noise characterization study. This GaN p-n diode has a similar structure as Figure 1a, except that an 80 nm undoped pseudomorphic In 0.07 Ga 0.93 N layer has been inserted on the cathode side, and the n-GaN drift layer thickness has been reduced to 150 nm. ...
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... GaN substrates by metal-organic chemical vapor deposition, the structure (from top to bottom) consists of a 10 nm p þþ contact layer, a 100 nm p-GaN layer (Mg: 2Â10 19 cm À3 ), a 250 nm n-GaN drift layer (Si: 2Â10 16 cm À3 ), and 2 μm n þ -GaN layer (Si: 4Â10 18 cm À3 ). Figure 1b shows the GaN p-n diode structure with an InGaN layer used for hole injection in the excess noise characterization study. This GaN p-n diode has a similar structure as Figure 1a, except that an 80 nm undoped pseudomorphic In 0.07 Ga 0.93 N layer has been inserted on the cathode side, and the n-GaN drift layer thickness has been reduced to 150 nm. The In 0.07 Ga 0.93 N layer is designed to produce pure hole injection under 390 nm UV illumination because this wavelength is beyond the absorption edge of GaN. ...
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... forward and reverse current-voltage characteristics of a typical baseline device (Figure 1a) at room temperature are shown in Figure 2. As shown in Figure 2a, the device turns on around 3.3 V (current density of 100 A cm À2 ). An ideality factor, n, of approximately 2 is measured from 2.1 to 2.6 V, indicating Shockley-Read-Hall (SRH) recombination-dominated current; n drops to 1.65 at a bias of 2.9 V, indicating the onset of diffusion-dominated current. ...
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... q is the electron charge, I is the bias current, M is the multiplication gain, and F is the excess noise factor. To further characterize the excess noise factor, GaN p-n diodes with a thin pseudomorphic In 0.07 Ga 0.93 N layer ( Figure 1b) were fabricated and measured in the dark and under 390 nm UV illumination. Figure 5a shows the reverse bias dark IV characteristics of a GaN p-n diode (100 μm radius) with InGaN cathode side hole (a) (b) (c) Figure 4. a) Measured dark current noise spectra for a baseline p-n diode as a function of reverse bias current, corresponding to the reverse bias voltages (red points) in part (b). ...
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... p ð0Þ and I n ðWÞ are the hole and electron currents, entering the two ends of the depletion region layer. In this coordinate system, x ¼ W at the top of the drift layer in Figure 1b and x ¼ 0 at the bottom. I is the total injected current and determined by [8] I ¼ I p ðxÞ þ I n ðxÞ ...
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Citations
... Avalanche breakdown in GaN power diodes was first reported in 2013 on a p-n junction fabricated on free-standing substrates. 2 Since then, there have been several other studies on it showing impact ionization coefficient measurements. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Other avalanche-based devices, such as IMPATT diodes and APDs, have also been reported. [21][22][23][24][25][26][27][28] Researchers began to measure impact ionization coefficients in GaN in the 1990s. ...
... 9,11,16,17 The different symbols indicate the experimental data reported by various groups. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] It is critical to note that only data from devices demonstrating an avalanche were collected. For different impact ionization coefficients, the projected breakdown electric field as a function of the doping concentration was plotted and compared to the reported experimental data, including our own data. ...
... Experimental data are all from non-punch through structures. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] design has a thinner drift region, it requires a greater electric field to trigger the multiplication of the carriers, and this is not included in Fig. 8. ...
Impact ionization coefficients play a critical role in semiconductors. In addition to silicon, silicon carbide and gallium nitride are important semiconductors that are being seen more as mainstream semiconductor technologies. As a reflection of the maturity of these semiconductors, predictive modeling has become essential to device and circuit designers, and impact ionization coefficients play a key role here. Recently, several studies have measured impact ionization coefficients. We dedicated the first part of our study to comparing three experimental methods to estimate impact ionization coefficients in GaN, which are all based on photomultiplication but feature characteristic differences. The first method inserts an InGaN hole-injection layer, the accuracy of which is challenged by the dominance of ionization in InGaN, leading to possible overestimation of the coefficients. The second method utilizes the Franz–Keldysh effect for hole injection but not for electrons, where the mixed injection of induced carriers would require a margin of error. The third method uses complementary p–n and n–p structures that have been at the basis of this estimation in Si and SiC and leans on the assumption of a constant electric field, and any deviation would require a margin of error. In the second part of our study, we evaluated the models using recent experimental data from diodes demonstrating avalanche breakdown.
... Recently, impact ionization coefficients from devices fabricated on bulk GaN substrates have been reported [7]- [11]. Cao et al. [7], [8] have measured the electron and hole impact ionization coefficients using both wavelength-selective photomultiplication and noise spectral density measurements based on p-n junctions with a thin pseudomorphic In 0.07 Ga 0.93 N layer grown on bulk GaN substrates, but no temperature dependence was reported. Ji et al. [9] obtained the impact ionization coefficients using the photomultiplication method based on p-on-n and n-on-p (with a buried p-GaN layer) diodes grown on bulk GaN substrates. ...
... For the 298 K α and β reported here, this results in α eff (298 K) = 6.496 × 10 −41 E 6.881 (8) where E is in V/cm and α eff is in cm −1 . The theoretical breakdown voltage of GaN non-punch through p-n diodes based on the effective impact ionization coefficients gives ...
The temperature dependence of the electron and hole impact ionization coefficients in GaN has been investigated experimentally. Two types of p-i-n diodes grown on bulk GaN substrates have been fabricated and characterized, and the impact ionization coefficients for both electrons and holes have been extracted using the photomultiplication method. Both the electron and hole impact ionization coefficients decrease as the temperature increases. The Okuto-Crowell model was used to describe the temperature dependence of the electron and hole impact ionization coefficients. Based on the measured impact ionization coefficients, the temperature dependence of the breakdown voltage of GaN non-punch through p-n diodes can be predicted; good agreement with experimentally reported results is obtained.
Wide and ultrawide-bandgap (U/WBG) materials have garnered significant attention within the semiconductor device community due to their potential to enhance device performance through their substantial bandgap properties. These exceptional material characteristics can enable more robust and efficient devices, particularly in scenarios involving high power, high frequency, and extreme environmental conditions. Despite the promising outlook, the physics of UWBG materials remains inadequately understood, leading to a notable gap between theoretical predictions and experimental device behavior. To address this knowledge gap and pinpoint areas where further research can have the most significant impact, this review provides an overview of the progress and limitations in U/WBG materials. The review commences by discussing Gallium Nitride, a more mature WBG material that serves as a foundation for establishing fundamental concepts and addressing associated challenges. Subsequently, the focus shifts to the examination of various UWBG materials, including AlGaN/AlN, Diamond, and Ga2O3. For each of these materials, the review delves into their unique properties, growth methods, and current state-of-the-art devices, with a primary emphasis on their applications in power and radio-frequency electronics.
This paper is dedicated to discussing the physics and applications of avalanche on III-Nitrides, primarily using Gallium Nitride as the example. Understanding the breakdown phenomenon in wide bandgap materials is of great interest to the device and circuit community as it directly impacts design and applications with these emerging semiconductors. In this paper, first, we go over the various approaches that have been reported on estimating the impact ionization coefficients in GaN, then discuss about the estimation of the critical electric field for punch-through and non-punch-through designs, and, finally, go over two avalanche-based devices that we have recently demonstrated.
