A self-aligned gate AlGaAs/GaAs heterostructure field-effect transistor with an ion-implanted buried-channel for use in high efficiency power amplifiers

In this paper we report on a self-aligned gate buried-channel Al0.22Ga0.78As/GaAs heterostructure field-effect transistor (BC-HFET). The BC-HFET comprises a selectively ion-implanted channel and an undoped i-AlGaAs surface layer. In order to realize the buried channel heterostructure, a combined process of ion-implantation and epitaxial growth is developed. The postimplantation annealing before the epitaxial growth successfully reduces the interdiffusion at the heterointerface between the ion-implanted GaAs channel and the AlGaAs surface layer. The BC-HFET overcomes the disadvantages of a low breakdown voltage which exists in conventional self-aligned gate MESFETs. The BC-HFET exhibits a high breakdown voltage of 8 V and a high Schottky barrier height of 0.75 eV. The l-mm-wide power BC-HFET demonstrates an output power of 18.2 dBm and a drain efficiency of 50% at a low adjacent channel leakage power of -59 dBc for a 1.9-GHz pi/4-shifted quadrature phase shift keying (QPSK) modulated input, for use as Personal Handy-phone System handsets.