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ABSTRACT High-quality GaN was grown using gas-source molecular-beam epitaxy (GSMBE). The mobility of undoped GaN was 350 cm2/Vsec and the carrier concentration was 6x1016 cm-3 at room temperature. A GaN metal semiconductor field-effect transistor (MESFET) and an n-p-n GaN bipolar junction transistor (BJT) were fabricated for hightemperature operation. The high-temperature reliability of the GaN MESFET was also investigated. That is, the lifetime of the FET at 673 K was examined by continuous current injection at 673 K. We confirmed that the FET performance did not change at 673 K for over 1010 h. The aging performance of the BJT at 573 K was examined during continuous current injection at 573 K for over 850 h. The BJT performance did not change at 573 K. The current gain was about 10. No degradation of the metalsemiconductor interface was observed by secondary ion-mass spectrometry (SIMS) and transmission electron microscopy (TEM). It was also confirmed by using Si-ion implantation that the contact resistivity of the GaN surface and electrode materials could be lowered to 7x10-6 ohmcm2.

INTRODUCTION III-V nitrides, SiC and diamond, are very promising materials for electronic devices that can operate under high-temperature, high-power, and high-frequency conditions [1], since these materials have a high melting point, a wide bandgap, a high breakdown electric field, and a high saturation velocity [2]. Furthermore, they have very low onresistance during operation compared with Si devices. Several groups have reported on GaN electronic devices [3-5]. Regarding high-temperature operation devices, there have only been a few reports concerning transistors that can operate at temperatures of 673 K [3-7], and the reliability of the GaN metal semiconductor field effect transistor (MESFET) at high-temperature. We have recently investigated the GaN MESFET using gas-source molecular beam epitaxy (GSMBE) [8-11]. However, until now, no life test of the FET by continuous current-injection at 673 K for over 1010 h has been reported. Furthermore, there have been few reports concerning the bipolar junction transistor [12-15]. Pankov fabricated a hetero-bipolar junction transistor using n-type GaN and ptype SiC, since p-type GaN with a high carrier concentration was very difficult to grow. They obtained a high current gain and high-temperature operation at 533 K. We have also recently reported that a GaN n-p-n bipolar junction transistor can be operated at high temperature [15]. However, life test at 573 K for over 800 h has not been reported. This paper reports on the high-temperature reliability concerning a life test of a GaN MESFET at 673 K for over 1010 h, a life test of over 850 h at 623 K of an n-p-n bipolar junction transistor and Si-ion implantation technique for obtaing a low-contact resistivity.

EXPERIMENT PROCEDURE

F99W4.8

A GSMBE apparatus was described elsewhere [8]. Dimethylhydrazine (DMHy, ((CH3)2NNH2)) as a nitrogen source gas, and ammonia (NH3) as a nitrogen source gas, as well as Knudsen effusion cells for a s