Piezoelectric field determination in strained InGaAs quantum wells grown on [111]B GaAs substrates by differential photocurrent

Abstract

The measurement of the differential photocurrent (DP) generated in PIN GaAs diodes with embedded strained InGaAs quantum wells has allowed us to determine the fields both in the GaAs barriers, as well as in the InGaAs strained quantum wells. Based on an electroreflectance (ER) setup, this technique relies on the generated photocurrent and does not require detection of the reflected light. The field in the GaAs barriers is obtained from DP Franz–Keldysh oscillations at photon energies above the GaAs bandgap, while the piezoelectric field in the wells is deduced from a phase change in the DP spectra under flat-band conditions in the quantum wells (QW). With optical power illuminations of a few nW, the in-well screening in these structures becomes negligible. With just 35mVRMS of modulating signal added to the diode bias and without photovoltaic effects due to the bias control of the sample, uncertainties in field calculations are reduced. The piezoelectric field values obtained at room temperature in MQW structures with 10 wells of 12 and 18% In content are close to those obtained by similar related techniques. For higher In content (20, 25 and 30%), single quantum well structures were used, also allowing the confirmation of pyroelectric behavior of the structures. Besides, direct comparisons of simultaneously grown [100] and [111] samples clearly reveal the earlier relaxation of the first ones when their QW absorption feature disappears.