Next we focus on the crystal quality by carefully analysing the first order Raman peaks' lineshape. Figure shows the measured spectra (i.e., data points) for the InAs samples grown at -1.3V, -1.325V and -1.35V. Each spectrum in Figure is the average of all pixels in the corresponding low intensity Raman maps (shown in Figure ). A Lorentzian fit to the data is also plot, where an asymmetric lineshape is considered for the LO peak (see fitting details in the experimental section). By comparing the spectra, we see a clear red shift and broadening of the LO peak with increasing potential, while the TO peak barely changes. The fact that the TO peak is stable in peak position rules out any strain differences between samples.