Method of envelope functions and intervalley Gamma-X-z interaction of states in (001) III-V semiconductor heterostructures

The kp method is used to analyze the problem of intervalley Gamma-X-z inter action of conduction-band states in the (001) lattice-matched III-V semicon ductor heterostructures. A convenient basis for expansion of the wave funct ion is systematically selected and a multiband system of equations is deriv ed for the envelope functions which is then reduced to a system of three eq uations for three valleys (Gamma(1), X-1, and X-3) by using a unitary trans formation. Intervalley Gamma-X-z mixing is described by short-range potenti als localized at heterojunctions. The expressions for the parameters determ ining the Gamma-X-z mixing strength explicitly contain the chemical-composi tion profile of the structure since mixing is naturally stronger for abrupt heterojunctions than for structures with a continuously varying chemical c omposition. It is shown that direct Gamma(1)-X-1 interaction of comparable strength to the Gamma(1)-X-3 interaction exists. This must be taken into ac count when interpreting tunnel and optical experiments since the X-1 valley is substantially lower in energy than the X-3 valley. (C) 2000 MAIK "Nauka / Interperiodica".