ranging from 20 nm up to 120 nm). Further information about the sample properties can be found in Ref. . Due to the textured structure we suppose that an electronic disorder potential is primarily caused by depletion of carriers, e.g. aluminum donor bound excitons [^1], due to interface band bending at grain boundaries [@Orton.1980]. (see Appendix \[sec:experiment\_disorderorigin\] for details).

![(color online) (a)-(d): Excitation power series of the far-field PL emission in a linear false color scale for $T = 10~{\mathrm{K}}$ and a detuning of $\Delta = -30~{{\mathrm{m}} {\mathrm{e}} {\mathrm{V}}}$. The excitation power is normalized to the condensation threshold $P_{{\mathrm{th}}}$. (e) $I_P(k)$ profiles of the condensate are extracted. These are integrated over the energy range $\Delta E$ marked by the white lines in the far-field emission pattern. The PL intensity for each power is normalized to the mean value of each $I_P(k)$ profile.[]{data-label="fig:Disorder"}](./{fig_Disorder_Images_10K_30meV_7.pdf}){width="0.9\hsize"}

Figures \[fig:Disorder\](a)-(d) show the excitation power dependence of the PL $k$-space emission pattern for $T = 10 \, {\mathrm{K}}$ and detuning $\Delta = -30 \, {{\mathrm{m}} {\mathrm{e}} {\mathrm{V}}}$. We deduce a polariton effective mass of $m=4.4 \times 10^{-5}~m_{{\mathrm{e}}}$ ($m_{{\mathrm{e}}}$: free electron mass) from the dispersion of the lower polariton branch (LPB) (not shown here). The excitation power density 