The effect of /spl gamma/-ray exposure on the electrical characteristics of nickel/n-GaN Schottky barrier diodes has been investigated using current-voltage (I-V), capacitance-voltage (C-V), and deep-level transient spectroscopy (DLTS) measurements. The results indicate that /spl gamma/-irradiation induces an increase in the effective Schottky barrier height extracted from C-V measurements. Increasing radiation dose was found to degrade the reverse leakage current, whereas its effect on the forward I-V characteristics was negligible. Low temperature (/spl les/50) post-irradiation annealing after a cumulative irradiation dose of 21 Mrad(Si) was found to restore the reverse I-V characteristics to pre-irradiation levels without significantly affecting the radiation-induced changes in C-V and forward I-V characteristics. Three shallow radiation-induced defect centers with thermal activation energies of 88 104 and 144 meV were detected by DLTS with a combined production rate of 2.12 /spl times/ 10/sup -3/ cm/sup -1/. These centers are likely to be related to nitrogen-vacancies. The effect of high-energy radiation exposure on device characteristics is discussed taking into account possible contact inhomogeneities arising from dislocations and interfacial defects. The DLTS results indicate that GaN has an intrinsically low susceptibility to radiation-induced material degradation, yet the effects observed in the Schottky diode I-V and C-V characteristics indicate that the total-dose radiation hardness of GaN devices may be limited by susceptibility of the metal-GaN interface to radiation-induced damage.

This paper shows the application of simple dc techniques to the temperature-dependent characterization of AlGaN/ GaN HEMTs in terms of the following: 1) thermal resistance and 2) ohmic series resistance (at low drain bias). Despite their simplicity, these measurement techniques are shown to give valuable information about the device behavior over a wide range of ambient/channel temperatures. The experimental results are validated by comparison with independent measurements and numerical simulations.

Transient capacitance measurements of Schottky diodes fabricated on nominally undoped n-type GaN exposed to 60Co gamma irradiation indicate the introduction of two defect levels with thermal activation energies of 89±6 and 132±11 meV. While the emission characteristics of these defects manifest significant broadening, their parameters are consistent with reported electron-irradiation-induced nitrogen-vacancy related centers. Three deep-level defects present before irradiation exposure with activation energies of 265, 355, and 581 meV were found to remain unaffected for cumulative gamma-ray doses up to 21 Mrad(Si).

Anisotropic carrier transport properties of unintentionally doped InAs/InAs_0.65Sb_0.35 type-II strain-balanced superlattice material are evaluated using temperature- and field-dependent magnetotransport measurements performed in the vertical direction on a substrate-removed metal-semiconductor-metal device structure. To best isolate the measured transport to the superlattice, device fabrication entails flip-chip bonding and backside device processing to remove the substrate material and deposit contact metal directly to the bottom of an etched mesa. High-resolution mobility spectrum analysis is used to calculate the conductance contribution and corrected mixed vertical-lateral mobility of the two carrier species present. Combining the latter with lateral mobility results from in-plane magnetotransport measurements on identical superlattice material allows for the calculation of the true vertical majority electron and minority hole mobilities; amplitudes of 4.7 $\times {10}^3$ cm²/V s and 1.60 cm²/V s are determined at 77 K, respectively. The temperature-dependent results show that vertical hole mobility rapidly decreases with decreasing temperature due to trap-induced localization and then hopping transport, whereas vertical electron mobility appears phonon scattering-limited at high temperature, giving way to interface roughness scattering at low temperatures, analogous to the lateral electron mobility but with a lower overall magnitude.

Design of practically realizable unipolar HgCdTe nBn photodetectors has been studied in detail by numerical analysis. The simulations reported herein reveal that, by optimization of barrier doping, dark current levels can be reduced and collection efficiency substantially improved. It is shown that p-type doping of the barrier layer can significantly reduce the effective potential barrier arising from the valence band offset between the absorber and barrier regions, thus enabling HgCdTe nBn detector operation under near zero-bias conditions. However, relatively high electric fields in the space charge regions near the barrier/absorber interface result in enhanced trap-assisted Shockley–Read–Hall thermal generation. Our calculations indicate that nBn HgCdTe detectors with barriers engineered by use of HgTe/Hg_0.05Cd_0.95Te superlattices have, potentially, substantially better valence band alignment without the need for p-type doping.