OPTICAL DETERMINATION OF CARRIER DENSITY IN PSEUDOMORPHIC ALGAAS INGAAS GAAS HETERO-FIELD-EFFECT TRANSISTOR STRUCTURES BY PHOTOLUMINESCENCE

A photoluminescence (PL) analysis of a highly degenerate two-dimensional electron gas (2DEG) in pseudomorphic modulation-doped AlGaAs/InGaAs/GaAs transistor structures is reported. The PL response from samples with one or two populated electron subbands is dominated by one or two spectral bands, respectively, with a high-energy intensity cutoff. The spectral width varies linearly with the measured 2DEG sheet density n(s) or with a Schottky barrier depletion voltage, which directly reflects the two-dimensional density of states (2DDOS) below the Fermi level. We used the effective electron mass from cyclotron resonance experiments to evaluate the 2DDOS and can thus directly determine n(s) from the spectral width via the 2DDOS. Independent n(s) values were obtained from Shubnikov-de Haas measurements and agree excellently with n(s) values from PL.