Tunable barrier heights and band discontinuities via doping interface dipoles: An interface engineering technique and its device applications

Abstract

We present, for the first time, a technique to effectively tune barrier heights and band discontinuities at semiconductor heterojunctions using doping interface dipoles (DID). The DID consists of two ultrathin ionized donors and acceptor sheets in situ grown within 100 Å of the heterointerface by MBE. Using a DID the photocollection efficiency of an AlGaAs/GaAs abrupt heterojunction has been increased by one order of magnitude. Detailed investigations show the importance of nonequilibrium and hot electron transport effects and tunneling in heterostructures with DIDs. Several new applications of this concept are discussed. A DID can be used to convert a type I heterojunction in a type II or staggered heterojunction. A DID at the heterointerfaces of superlattice and staircase avalanche photodiodes can further enhance the ionization of electrons at the conduction band steps. The speed of heterojunction photodetectors such as the ones employing InP/Ga_0.47In_0.33As can be enhanced by a DID without requiring grading of the interface. The effects of doping fluctuations in the charge sheets of the DIDs on transport properties across the heterointerface are also briefly discussed. The DID represents a new interface engineering technique in the sense that it allows one to selectively engineer the energy band diagram of a heterostructure within less than 100 Å from the heterointerface and as such has important implications for the physics of interfaces and the design of novel devices.