TABLE OF CONTENTS The last twenty years has seen GaAs material being used increasingly for many microwave devices including the field effect transistor. There are, however, many other compound semiconductors which should give considerable gain, noise figure and higher frequency advantages over GaAs. These materials include indium phosphide (InP) and the ternary and quaternary compounds such as Ga xIn 1 ?xAs and Ga xIn xAs ySb 1 ?y. Of the ternary compounds InPAs appears to be most likely to give substantial frequency of operation improvement and GaInAs to give substantial gain and noise figure improvement, particularly at the higher frequencies. However, in order to reach operating frequencies approaching 50 GHz or so narrow gate length devices are still needed and the technology and ingenuity of the device designer then limits the device performance.
In order to substantially increase the maximum frequency of oscillation it is necessary to develop new transistor structures which, although having the advantages of the FET (that is being majority carrier devices), also have some of the advantages of the bipolar transistor such as very high transconductance. One of the most promising structures receiving much attention at the present time is the permeable base transistor which may ultimately have a maximum frequency of oscillation greater than 1000 GHz compared with typical values of only 80 GHz for a conventional 0.5 ?m gate length GaAs FET.
Indium phosphide (InP) has electronic properties very similar to those...
