High temperature performance of recent GaAs transistors

Recent advances in the preparation of GaAs material and in GaAs technology have enabled diffused-base, alloyed emitter GaAs transistors to be constructed which exhibit fT\´s in excess of 1 Gc. Because of the greater band-gap (1.38 eV) of GaAs, these transistors should be operable at temperatures exceeding 350°C. The physical method of fabrication, however, limits these experimental transistors to a junction operating temperature of slightly greater than 200°C. In this paper the techniques employed to construct these transistors will be described; the limitations imposed on operating temperature by state-of-the-art technology and means of overcoming these limitations will be discussed. Data will be presented to characterize these GaAs transistors at elevated temperatures and will show that high frequency current gain (hfe) varies only slightly with temperature. Graphs displaying the variation of the other "h" parameters with temperature will be given, as will plots of the behavior of VCE(SAT)and Icowith increasing temperature. The significance of the high temperature stability of these GaAs transistors as it applies to both small signal and high power devices will be indicated.