Optical characterisation on the effect of doping concentration in InGaAs/InP HEMT structures

Photoluminescence and Raman scattering measurement were carried out to stud y the effect of varying the dopant concentration (N-D) in the InP donor lay er of In0.53Ga0.47As/InP high-electron mobility transistor (HEMT) structure s. Assuming that the donors are fully ionized, the carrier concentration in the InGaAs channel layer was found to increase when the doping concentrati on in the donor layer was increased. From PL, a red shift is observed for t he E-1-HH1 peak with increasing doping concentration. Both E-1-HH1 and E-2- HH1 transitions can only be observed for doping concentration greater than 1.5 x 10(18) cm(-3). Raman characteristic was clearly seen with the two LO modes (InAs-like LO and GaAs-like LO) located at 226 cm(-1) and 268 cm(-1), respectively. The coupled mode between the InGaAs longitudinal optical pho nons and the electrons in the InGaAs channel was observed to shift continuo usly to a lower wave number with the increase in the value of N-D in the In P donor layer. The correlation between the observed Raman shift with the ca rrier concentration in the channel layer allows for non-destructive charact erization of HEMT structures. (C) 2000 Elsevier Science B.V. All rights res erved.