A High Power Gaas Schottky Barrier Impatt Diode in 30GHZ Band

Abstract

INTRODUCTIONShortly after the first observation of microwave oscillation from Si IMPATT diodesl), F. A. Brand et al.2) and J. C. Iyvin3) found the same phenomena on GaAs diodes. Subsequently, L. D. Armstrong4 succeeded in CW operation of p n GaAs IMPATT diodes and found that they operated with high efficiency and low noise. However, the thermal conductivity of GaAs is about one third of that of Si, so that the p+n diode structure has apparently a disadvantage fo heat dissipation. In order to reduce the thermal resistance, C. K. Kim et al.5) made Shottky metal-n-n+ diodes and succeeded in obtaining high power, high efficiency oscillation. The best results reported to date are 4.5 W at 5.5GHz with an efficiency of 13 %6) and 2.1 W at 9.2 A9z with an efficiency of 9 %7).As for the noise of the diode, P. A. Levine et al.obtained an AM noise of -140 dB at C-band with a p+n IMPATT diode. These results are superior to those of conventional Si IMPATT diodes, and GaAs are expected to be capable of a higher efficiency, lower noise microwave source.The present paper discusses the method to obtain high efficiency, high power IMPATT diodes in 30 GHz band using a GaAs Schottky barrier. For the IMPATT diodes in 30 GHz band, a thin high-quality GaAs epitaxial layer is required. In the experiment, Sn-doped epitaxial layers were grown on Sn-doped substrates by the liquid phase epitaxy. In order to form a Schottky barrier, Pt, Mo and Au were successively evaporated on the chemically etched surface of the epitaxial layer. The lower electrode to the diode was made by plating copper on the evaporated Pt-Mo-Au Schottky metal and was used as a heat sink (IHS diode). By this method, the thermal resistance was reduced to close to the theoretical value. In ordpr to increase the reliability of the diode, a quartz stud was fixed near the diode and an Au-wire was bonded on both the stud and the upper electrode of the diode (stud diode). On the diode without the stud, the maximum power and efficiency obtained were 840 mW and 13.5 %, while on the diode with the stud, 735 mW and 12.4 % were obtained.The temperature dependence of the diode characteristics was also investigated and the temperature dependence of the oscillation frequency was found to be small as -100 --200 kHz/0C, which was theoretically well understood. DESIGN CONSIDERATIONAccording to the computer simulation on GaAs IMPATT diodes9) , the thickness of the n-layer is determined by the Read condition. The electron concentration of the n-layer is determined so as to operate the diode under the just-punch-through condition at the steady state. When it is assumed that the junction temperature is 2000C and the electron saturation velocity is ACKNOWLEDGEMENTSThe authors wish to thank H