Naohito Yoshida

Thermal stability of AlInAs/GaInAs/InP heterostructures

The origin of the thermal instability of the AlInAs/GaInAs system is identified and a novel method to recover the thermal degradation is also demonstrated. The thermal diffusion of fluorine into the Si‐doped AlInAs layer is found to be the main cause of the electrical deterioration of this system. This finding has led to a method to recover the thermal degradation by purging the fluorine off using the reannealing in the ultrahigh‐vacuum condition. This method is now potentially becoming a good candidate as a tip for the AlInAs/GaInAs devices fabrication including laser diode and high electron mobility transistor.

Overview of recent development of HEMTs in the mm-wave range

Abstract Recent expansion in the demand for high frequency applications requires new transistors with better performance than the MESFETs, especially in the upper-microwave and mm-wave frequency ranges. To realize better transistors than the MESFET by utilizing features of the heterostructure, high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) are being developed. GaAs pseudomorphic HEMTs (PHEMTs) are currently the main type of low noise transistors being used in various microwave and mm-wave systems. Very low noise figures of 1.5 dB at 60 GHz and 2.1 dB at 94 GHz are achieved with GaAs PHEMTs. Furthermore, InP HEMTs, with better noise performance than GaAs PHEMTs, are being developed to replace the latter. State of the art noise figures for InP HEMTs are, for example, 0.8 dB at 60 GHz and 1.2 dB at 94 GHz. GaAs based power HEMTs show higher efficiencies than competing MESFETs for frequencies over 10 GHz, and are comparable to them below 10 GHz. In the higher frequency range, the state of the art in the output power of HEMTs gives a −6 dB/octave line connecting 4W at 20 GHz and 0.1 W at 100 GHz. As there are still reliability problems yet to be solved with the low noise InP HEMTs and the power HEMTs, further study of degradation mechanisms in AlInAs/InGaAs/InP systems, r.f. operation testing of really high power HEMTs, systematic reliable data, etc. would be necessary for them to be accepted as having been established to be reliable devices.

A 68% efficiency, C-band 100W GaN power amplifier for space applications

This paper describes a high efficiency (68%), high output power (100W), high reliability GaN HEMT amplifier for C-band space applications. The high efficiency is achieved by 2nd-harmonic frequency (2fo) tuning circuits in the input and output matching circuits. The input circuit uses open-ended stubs located nearby FET gate terminals for setting the 2fo reflection-phase at the optimum phase. In the output circuit, the optimum 2fo reflection phase is realized using three transmission-line transformers while matching loss is kept low at fundamental frequency. In addition, a 3000 hours RF overdrive life test reveals that an estimated mean time to failure (MTTF) is 1×107 hours at 150°C channel temperature, proving that the amplifier has sufficient reliability for space applications. To the best of our knowledge, the efficiency of 68% is the highest of 100-W class C-band amplifiers ever reported, and is also comparable to that of commercially available traveling wave tube amplifiers.

Improvement of InP Crystal Quality on GaAs Substrates by Thermal Cyclic Annealing

We have studied the effect of thermal cyclic annealing (TCA) on the crystal quality improvement of MOCVD grown InP on GaAs substrates. The crystal quality has been evaluated by the etch pit density (EPD), X-ray diffraction and photoluminescence (PL) measurement. It is found that the TCA is effective in reducing the dislocation density, and that the annealing at 700°C is essential to confine the point defects near the InP/GaAs interface. The EPD is reduced from 6×107 cm-2 to 3×107 cm-2, and the defect-related PL peak intensity is decreased below the residual level in the 5 µm-thick InP on GaAs.

A 60 GHz-band ultra low noise planar-doped HEMT

An ultra-low-noise AlGaAs/InGaAs HEMT (high electron mobility transistor) with a 0.15- mu m T-shaped gate and an Si planar-doped layer has been developed for millimeter-wave systems. The HEMT showed an extremely reduced minimum noise figure of 1.6 dB and a high associated gain of 6.5 dB at 60 GHz. The noise figure is the lowest value ever reported for the AlGaAs/InGaAs pseudomorphic HEMT.<<ETX>>

Degradation mechanisms of GaAs PHEMTs in high humidity conditions

We have studied the degradation mechanism of AlGaAs/InGaAs pseudomorphic HEMTs (PHEMTs) under high humidity conditions. The samples show a decrease in maximum drain current (Imax) and positive shift in threshold voltage (Vth). It was found that the Vth shift depends on gate orientation, caused by a piezoelectric effect due to stress change near the gate. Cross-sectional TEM images from the deteriorated devices reveal the existence of a damaged recess surface region and a peeling of the passivation film (PF). At the interface between the PF and AlGaAs surface, diffusion of Ga, As and Al into the PF was observed by SIMS. From these results, degradation of the PHEMT has two main mechanisms: positive shift in Vth due to stress change under the gate which might be caused by the peeling of the PF, and a decrease in Imax due to surface degradation at AlGaAs recess regions caused by diffusion phenomena of Ga,As and Al. The pre-deposition treatment effectively suppresses the degradation of PHEMTs under high humidity without degradation of high frequency performance.

High gain and high efficiency K-band power HEMT with WSi/Au T-shaped gate

We have developed WSi/Au T-shaped buried gate pseudomorphic HEMT with the good uniformity of recess current by using a selective etching process and with a high off-state break down voltage of over 19 V. A 1.4 W output power has been obtained with a power-added efficiency of 55.6% and an associated gain of 9.2 dB under high voltage operation of Vd=10 V at 18 GHz. This is the highest gain and efficiency achieved by a single FET chip with over a watt output power at this frequency.

Corrosion-induced degradation of GaAs PHEMTs under operation in high humidity conditions

Abstract We have comprehensively investigated the degradation mechanism of AlGaAs/InGaAs pseudomorphic high-electron-mobility transistors (PHEMTs) under operation in high humidity conditions. PHEMTs degradation under high humidity with bias consists of a decrease in maximum drain current (Imax) caused by a corrosion reaction at the semiconductor surface at the drain side. The decrease in Imax is markedly accelerated by the external gate–drain bias (Vdg). This originates from a reduction in the actual activation energy (Ea0) by Vdg. The degradation depends on the surface treatment prior to deposition of the SiNx passivation film. The reduction of As-oxide at the SiNx/semiconductor interface suppresses the corrosion reaction.

Degradation mechanisms of GaAs PHEMTs under operation in high humidity conditions

We have comprehensively investigated the degradation mechanism of AlGaAs/InGaAs pseudomorphic highelectron- mobility transistors (PHEMTs) under operation in high humidity conditions. The degraded samples under high humidity condition with bias show a decrease in maximum drain current (Imax).The decrease of Imax is accelerated with increasing drain voltage, temperature and humidity. The PHEMT degradation is caused by corrosion reaction at the semiconductor surface at drain side. The rate of corrosion degradation is increased by RH3. Higher Vgd decreases the actual activation energy for corrosion. The degradation depends on surface treatment prior to deposition of a SiNx passivation film.The reduction of As-oxide at SiNx/semiconductor interface might suppress the corrosion reaction.

Isothermal capacitance transient spectroscopy of pseudomorphic high-electron-mobility transistors

The surface electronic properties of AlGaAs/InGaAs pseudomorphic high-electron-mobility transistors were investigated by isothermal capacitance transient spectroscopy (ICTS) and gate-leakage current characteristic measurements. Both hole- and electron-like trap spectra were observed by ICTS measurements on gate–source/drain capacitance. We observed enhancement of leakage current and drastic change of static and transient capacitance behavior around a pinch-off voltage. The leakage characteristics and ICTS results were explained in terms of a surface states model.