No abstract

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.Index Terms-Gallium compounds, microwave power transistors, MODFETs, power HEMTs, semiconductor-device measurements, semiconductor-device thermal factors, wide bandgap semiconductors, III nitrides, III-V semiconductors.

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).

Transport properties of two distinct electron species in indium nitride grown by molecular beam epitaxy (MBE) have been measured. Variable field Hall and resisitivity voltages were used in a quantitative mobility spectrum analysis (QMSA) to extract the concentrations and mobilities of the two electron species, attributed to the bulk electrons and a surface accumulation layer. Single magnetic field data corresponds to neither electron species. The bulk electron distribution has an extracted average mobility of 3570 cm 2 /(V s) at 300 K, which rises to over 5100 cm 2 /(V s) at 150 K. Bulk electron concentration in the sample is 1:5 Â 10 17 cm À3 . The surface electrons have a higher sheet charge density and an order of magnitude lower average mobility than those in the bulk.

We have investigated the pH and ion sensitivity of AlGaN/GaN heterostructure devices; these devices are sensitive to the ion concentration rather than to the pH of the solution. Sheet resistance as a function of pH for calibrated pH solutions and dilute NaOH, HCl, KOH, and NaCl showed an increase as a function of ionic concentration, regardless of whether the pH was acidic, basic, or neutral. An increase in resistance corresponds to accumulation of negative ions at the AlGaN surface, indicating device selectivity toward the negative ions. We attribute this to the formation of a double layer at the liquid/semiconductor interface.