Optical studies of two-dimensional electron gas in an InGaAs/AlGaAs pseudomorphic high electron mobility transistor structure

We present the studies of two-dimensional electron gas (2DEG) in an InGaAs/AlGaAs pseudomorphic high electron mobility transistor (pHEMT) structure using photoluminescence (PL), photoreflectance (PR), photoconductivity (PC) and Hall measurements in the temperature range 10–300 K. The energies of intersubband transitions (11H, 21H and 22H) can be determined through the experimental results and theoretical fitting data of PC, PL and PR. The Fermi level is extracted from the curve-fitting data of PL and PR with the subband filling effect taken into account. It is shown that the Fermi level reaches the 2nd electron subband E2 and thus the 1st electron subband E1 is nearly fully occupied so that the 11H PR absorption feature becomes almost invisible due to the severely suppressed probability of transition to E1. The curve-fitting data of PL and PR also give the carrier concentration of 2DEG, and the value is found to be in great consistency with the Hall data. Our work as a whole exhibits consistent results in the 2DEG properties through various methods and clearly shows that optical technologies (PL and PR) provide useful alternatives for contactless, non-destructive characterization of the 2DEG carrier concentration.