18.5-dB Gain at 18 GHz with a GaAs permeable base transistor

Permeable base transistors have recently been fabricated using organometallic chemical vapor deposition (OMCVD) with a gain of 18.5 dB at 18 GHz. This extrapolates to an
f_{\max}
of 150 GHz which is comparable to the best previous result. Secondary ion mass spectrometry (SIMS) analysis shows that there is a large concentration of undesired impurities in the grating region of these recent devices. It is quite probable that better performance can be achieved in future devices if those impurities can be eliminated.