Indium arsenide-based bipolar transistors grown by molecular beam epitaxy

Large carrier mobilities and large electron saturation velocity make InAs a promising material for high speed devices. Additionally, the low band gap is useful for low power applications. By applying bipolar transistors, high frequency, high-speed devices and applications can be easily realized. Thus InAs-based bipolar transistors are studied extensively in this work. InAs-based bipolar junction transistors (BJTs) with current gains (beta) up to 400 have been achieved. The physics of beta in InAs BJTs is studied by estimating the emitter injection efficiency (gamma), the base transport factor (alphaT), and the minority carrier (electrons) diffusion length in the base (LB).; AlInAs/InAs and InAsP/InAs HBTs are realized. InAs based HBTs have higher current gain than BJTs with similar structures and same doping profiles. Advantages of HBTs over BJTs are shown by a comparison of the electrical characteristics of AlInAs/InAs HBTs and InAs BJTs.; The development of a high frequency transistor is dependent on the insulating quality of the substrate, in order to reduce large leakage into the collector. However, presently no semi-insulating substrates that are lattice matched to InAs exist. This necessitates metamorphic growth of InAs bipolar junction transistors (BJTs) on semi-insulating substrates, such as GaAs or InP. The metamorphic InAs BJTs grown on InP and GaAs substrates are realized, studied and compared with the InAs BJTs lattice-matched grown on InAs substrates. The experimental results show that the surfaces are smoother and the leakage currents for base-collector junctions (Ir's) are smaller for the metamorphic BJTs with thicker buffer layer, although the surfaces are still rougher and Ir's are higher compared to InAs-based BJTs due to the lattice mismatch. Surprisingly, the current gains of all the metamorphic BJTs are not sensitive to the buffer layer thickness and comparable to the lattice-matched grown BJTs on InAs. They all have the current gains between 50 and 70 at room temperature. By comparing the metamorphic InAs BJTs on GaAs substrates and InP substrates, it is surprisingly discovered that the surface of the materials grown on GaAs substrates are smoother, which was not expected since the misfit between InAs and GaAs is twice greater than that between InAs and InP. This may be due to the difficulty of growing phosphides on arsenides. However, the devices on InP substrates exhibit better electrical characteristics than those on GaAs substrates. The success of fabricating InAs bipolar transistors on semi-insulating GaAs and InP substrates makes InAs-based high frequency and high speed devices possible.