Ultrahigh Be Doping of Ga sub (0.47) In sub (0.53) As by Low Temperature Molecular Beam Epitaxy

We present the results of a study of highly Be doped Ga sub (.47) In sub (.53) As grown on InP as a function of growth temperature. A doping level of 5x10 sup (20) cm sup (-3) has been reached at a growth temperature of 365C. This is about 10 times greater than the highest previously reported levels of intentional p-type doping in InGaAs. All of the samples for this study were grown by a version of gas source molecular beam epitaxy (GSMBE) in which decomposed AsH sub 3 and PH sub 3 are used for the generation of As sub 2 and P sub 2 beams and elemental source effusion cells were used for the generation of Ga, In and Be. Substrate temperatures during growth ranged from 365C to 505C. The maximum doping was found to be extremely growth temperature dependent. For each growth temperature a value of N sub a - N sub d is reached for which a further increase in Be flux fails to increase N sub a - N sub d. The use of reduced growth temperature to attain high doping in the base of InGaAs/InP heterostructure bipolar (HBT) transistors has permitted the demonstration of the highest speed bipolar transistors ever reported. We illustrate this with a HBT with a base doping of p = 1x10 sup (20) cm sup (-3) current gain B=54 and unity current cutoff frequency, f sub t = 140GHz.