Absorption Spectroscopy of the Continuous Transition from Heavily Modulation Doped to Undoped InGaAs Single Quantum Well.

In this letter we present the first investigation by direct differential absorption of the continuous transition of a single InGaAs quantum well from modulation doped (N~8x10 sup 11 cm sup -2) to undoped (N~ 0). We observe a progressive quenching of the optical transition at the first subband and red shifts and broadening at higher subbands. We show that these effects originate from phase-space filling and Stark effect. They give direct in situ information on important parameters of the 2D electron gas in field effect structures.