Article comprising a 'ballistic' heterojunction bipolar transistor

Abstract

The disclosed heterojunction bipolar transistor, to be referred to as the 'coherent' transistor (CT), is capable of providing gain above the conventionally defined cut-off frequencies f.sub.T and f.sub.max. Substantially, mono-energetic (average energy .DELTA.) carriers are injected in beam-like fashion into the base, with kT<.DELTA.<hv.sub.opt, where k, T and h have their conventional meaning, and v.sub.opt is the frequency of the lowest relevant optical phonon in the base of width W.sub.B. Exemplarily, W.sub.B is about 100 nm, .DELTA. is about 20 meV, the CT comprises Si.sub.1-x Ge.sub.x or III/V material, with the base being doped n-type. The CT utilizes substantially collisionless minority carrier transport through the base, and is designed such that, at an operating temperature which typically is .ltorsim.77K, the variance of the average base transit time (.DELTA..tau..sub.B) is much less than the base transit time .tau..sub.B, typically less than 0.5 .tau..sub.B, preferably about .tau..sub.B /5 or less. Transistors according to the invention typically will have an operating frequency in the range 100 GHz-1THz, and can be advantageously used in many areas of technology, e.g., high speed computing or communications.