Delta doping of III–V compound semiconductors: Fundamentals and device applications

Abstract

Delta-function-like doping profiles can be obtained in semiconductors by growth-interrupted impurity deposition during molecular-beam epitaxy. The spatial localization of dopants is assessed by the capacitance–voltage profiling technique and secondary ion mass spectroscopy which yield profile widths of 20 and 37 Å for Be δ-doped GaAs grown at 500 °C, respectively. The diffusion coefficients of Si, Be, and C in GaAs and of Si in AlxGa1−xAs are determined and diffusion is shown to be negligible at low growth temperatures. At elevated growth temperatures, dopant redistribution occurs during epitaxial growth. The redistribution is shown to be due to (i) diffusion of dopants and (ii) Fermi-level pinning induced segregation of dopants along the growth axis. Fermi-level pinning induced segregation of dopants is a novel mechanism which results in a redistribution of dopants predominantly toward the growing surface due to electrostatic attraction of dopants and carriers localized in surface states. This mechamism is shown to be relavant at elevated growth temperatures of ≥600 °C. Electronic devices such as homostructure and heterostructure field-effect transistors which employ the δ-doping technique have a number of advantages including (i) high carrier density, (ii) proximity between electron channel and gate electrode, (iii) large breakdown voltage of the gate, and (iv) reduced short-channel effects. In addition, high transconductances are obtained in such δ-doped field-effect transistors. The optical properties of doping superlattices are significantly improved using the δ-doping technique. Quantum-confined interband transitions in doping superlattices are observed for the first time in such improved doping superlattices. Furthermore, a tunable doping superlattice laser is demonstrated, which has a tuning range of 35 Å. The tunable doping superlattice laser has a potential tuning range of 220 Å and is a candidate for a tunable source in future optical communication systems.