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Defect origins and their propagation behavior were investigated in 25 μm thick homo-epitaxial GaN layers grown on ammono-thermal and void-assisted separation (VAS) substrates using multi-vector x-ray topography in both transmission and reflection geometries. Complex inclusions were identified and their microstructure was analyzed. Additionally, generation of threading dislocation clusters during epitaxial growth is analyzed. Various defects are delineated from the substrate vs epitaxial layers. Growth on the ammono-thermal substrate led to less defective and flatter epitaxial layers compared to the growth on the VAS substrate. Determining the origins and microstructure of defects is crucial toward developing defect mitigation strategies for reliable GaN devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Plasma etching of p-type GaN creates n-type nitrogen vacancy (VN) defects at the etched surface, which can be detrimental to device performance. In mesa isolated diodes, etch damage on the sidewalls degrades the ideality factor and leakage current. A treatment was developed to recover both the ideality factor and leakage current, which uses UV/O3 treatment to oxidize the damaged layers followed by HF etching to remove them. The temperature dependent I–V measurement shows that the reverse leakage transport mechanism is dominated by Poole–Frenkel emission at room temperature through the etch-induced VN defect. Depth resolved cathodoluminescence confirms that the damage is limited to first several nanometers and is consistent with the VN defect. [ABSTRACT FROM AUTHOR]

InAlN/GaN high electron mobility transistors were irradiated from the front side with 340keV protons to a dose of 5 × 1013 cm-2. Raman thermography showed that the irradiated devices had higher channel temperatures than unirradiated control devices, but only by ~10% under typical biasing conditions. Accordingly, the irradiated devices have higher thermal resistance (400°C/W) compared to reference devices (350°C/W), based on the slope of the power versus channel temperature line. However, increases of 42% in off-state drain breakdown voltage (VBR) and of >92% in critical voltage (Vcri) were observed for the proton irradiated HEMT. This is ascribed to the reduction of the peak electric field at the gate edges by ~50% through the introduction of negative trap charges created from vacancies generated by the proton irradiation. [ABSTRACT FROM AUTHOR]

A threshold reverse bias of ∼21 V was observed leading to a sharp increase in the gate current of AlGaN/GaN high electron mobility transistors biased at low source-drain voltage (5 V). The gate current increases by one to two orders of magnitude at this bias, corresponding to an electric field strength around 1.8 MV cm-1. The gate current increased by roughly five orders of magnitude after step-stressing the gate bias from 10 to 42 V in 1 V increments for 1 min at each bias. The drain current was also decreased by ∼20% after this step-stress cycle. The photoluminescence and electroluminescence intensity from the semiconductor is decreased along the periphery of the gate region after stressing and transmission electron microscopy shows a thin native oxide layer under the gate and this disappears as the gate metal reacts with the underlying AlGaN. [ABSTRACT FROM AUTHOR]

Multiple GaN nanowires produced by thermal chemical vapor deposition were employed as gas sensors for detection of hydrogen at concentrations from 200–1500 ppm in N2 at 300 K. Palladium coating of the wires improved the sensitivity by a factor of up to 11 at low ppm concentrations relative to uncoated controls. The GaN nanowires showed relative responses of ∼7.4% at 200 ppm and ∼9.1% at 1500 ppm H2 in N2 after a 10 min exposure. Upon removal of hydrogen from the measurement ambient, ∼90% of the initial GaN conductance was recovered within 2 min. Temperature dependent measurements showed a larger relative response and shorter response time at elevated temperature. The adsorption activation energy of the sensor was 2.2 kcal mol-1 at 3000 ppm H2 in N2. These sensors exhibit low power consumption (<0.6 mW) at 300 K. [ABSTRACT FROM AUTHOR]