ABSTRACT
High Electron Mobility Transistors fabricated from GaInAs/AlInAs modulation-doped structures currently exhibit the highest current gain cut-off frequency, highest maximum frequency of oscillation and lowest noise figure of any three terminal device. Inverted (GaInAs on AlInAs) and double-doped device structures have not been widely utilized in this material system because of the poor mobility of the two-dimensional electron gas formed at the inverted modulation-doped interface. This chapter discusses the degree of silicon segregation that occurs in AlInAs as a function of the substrate temperature, the improvement in the mobility of the 2DEG formed at the inverted interface grown with a low temperature spacer, the improvement in transfer efficiency obtained with the low temperature spacer, and device results from fabricated wafers utilizing these improved growth conditions. A technique in which the AlInAs spacer layer is grown at a reduced substrate temperature has been developed that allows for the growth of inverted structures with electron mobilities comparable to those achieved in normal structures.
