Akihisa Terano

Single-voltage-supply highly efficient E/D dual-gate pseudomorphic double-hetero HEMT's with platinum buried gates

Highly efficient enhance/depletion (E/D) dual-gate HEMTs for use in high-power linear amplifiers with a single biasing supply are demonstrated. These devices include platinum buried gates to realize a single biasing supply. A double-heterostructure and a GaAs/InGaAs/GaAs superlattice channel were adopted to obtain a good linearity and a large gain. An E/D dual-gate field effect transistors (FET) structure is also adopted to improve the gain and efficiency. High output power of 24 dBm, high power gain of 24 dB, and high power-added-efficiency of 46% for the gate width of 4-mm sample were obtained under conditions with a 1.5-GHz Japan Personal Digital Cellular (PDC) standard and with a +3.5 V single biasing supply.

Analysis of Leakage Current at Pd/AlGaN Schottky Barriers Formed on GaN Free-Standing Substrates

Analytical solutions based on the thin surface barrier (TSB) model were utilized to reproduce the measured current–voltage characteristics of Pd/unintentionally doped Al0.08Ga0.92N/compositionally graded AlGaN/n-GaN Schottky barrier diodes (SBDs) formed on GaN free-standing substrates. The TSB thickness (D) and the Schottky barrier height were used as fitting parameters, while the measured surface concentration of shallow donors was used as a constant. Since the resultant D was close to the value determined from the oxygen concentration profiles, the surface oxygen was concluded to be deeply-involved in the TSB formation.

Interdiffusion of magnesium and iron dopants in gallium nitride

The interdiffusion of magnesium and iron in gallium nitride (GaN), i.e., magnesium–iron interdiffusion, was investigated using magnesium-doped GaN layers on iron-doped GaN substrates. The investigation confirms that the magnesium–iron interdiffusion strongly depends on the concentrations of magnesium and iron, that is, it occurs when the iron and magnesium concentrations are high (magnesium: 2 × 1020 cm−3; iron: 2 × 1019 cm−3). It also confirms that diffused iron in the magnesium-doped GaN layer acts as a nonradiative recombination center in GaN.

Thick (>20 µm) and high-resistivity carbon-doped GaN-buffer layers grown by metalorganic vapor phase epitaxy on n-type GaN substrates

To improve the performance of GaN power devices, we have investigated the crystalline quality of thick (>20 µm) carbon-doped GaN layers on n-type GaN substrates and templates. The surface morphologies and X-ray rocking curves of carbon-doped GaN layers were improved by using GaN substrates. However, the crystalline quality degraded when the carbon concentration was too high (1 × 1020 cm−3), even in the case of GaN substrates. High breakdown voltages (approximately 7 kV under a lateral configuration) were obtained for the carbon-doped GaN layers on n-type GaN substrates when the carbon concentration was 5 × 1019 cm−3. These results indicate that lateral power devices with high breakdown voltage can be fabricated by using thick carbon-doped GaN buffer layers, even on n-type GaN substrates.

Characterization and modeling of bias-stressed InGaP/GaAs collector-up tunneling-collector HBTs fabricated with boron-ion implantation

To characterize and model the degradation of collector-up (C-up) heterojunction bipolar transistors (HBTs), we bias stress InGaP/GaAs C-up tunneling-collector HBTs (TC-HBTs) fabricated under various conditions for etching the collector mesas and of implanting boron ions into the extrinsic emitter. Contrary to the previous reports on reduction in collector current I/sub C/ of bias-stressed emitter-up HBTs fabricated with ion implantation, no I/sub C/ Gummel shift is observed in the case of C-up TC-HBTs, probably due to the lower damage resulting from the lower ion dosage. On the other hand, the base current of the bias-stressed C-up TC-HBTs increases with the decrease of the ion dose and with the increase of the collector mesa undercut under the collector electrode that is also used as an implant mask. We attribute the increased base current to the increased carrier recombination at the extrinsic base surface. Making the area of the emitter-base junction smaller than that of the base-collector junction-using electron-cyclotron resonance plasma etching together with lateral spreading of heavily implanted boron ions-results in a stable current gain even after a 1030-h testing at a junction temperature of 210/spl deg/C and a collector current density of 40/sup 2/kA/cm.