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

摘要

Photoluminescence and Raman scattering measurement were carried out to study the effect of varying the dopant concentration (N_D) in the InP donor layer of In_0.53Ga_0.47As/InP high-electron mobility transistor (HEMT) structures. Assuming that the donors are fully ionized, the carrier concentration in the InGaAs channel layer was found to increase when the doping concentration in the donor layer was increased. From PL, a red shift is observed for the E_1 -HH_1 peak with increasing doping concentration. Both E_1-HH_1 and E_2 -HH_1 transitions can only be observed for doping concentration greater than 1.5 ×10~18 cm~-3. Raman characteristic was clearly seen with the two LO modes (InAs-like LO and GaAs-like L0) located at 226 cm~-1 and 268 cm~-1, respectively. The coupled mode between the InGaAs longitudinal optical phonons and the electrons in the InGaAs channel was observed to shift continuously to a lower wave number with the increase in the value of N_D in the InP donor layer. The correlation between the observed Raman shift with the carrier concentration in the channel layer allows for non-destructive characterization of HEMT structures.