Pablo O. Vaccaro
Piezoelectric effect in InGaAs/GaAs
quantum wells grown on (n11)A-oriented
GaAs substrates (n=1, 2, 3, 4)
Abstract:Strained quantum wells (SQWs) of InGaAs play an important role in laser diodes, optical modulators and many other optoelectronic devices. These SQWs have been usually made on GaAs (100)-oriented substrates and do not show piezoelectric effect because crystal symmetry. We have grown InGaAs SQWs on GaAs (111)A, (211)A, (311)A, and (411)A-oriented substrates. High quality SQWs where obtained on GaAs (311)A and (411)A-oriented substrates. Moreover, (311)A-oriented SQWs showed an enhanced photoluminescence (PL) intensity, as compared to the (100)-oriented ones, suitable for laser diode applications.
The built-in electric field generated by the piezoelectric effect in (311)A-oriented SQWs was also studied. In contrast to SQWs grown on (100)-oriented substrates, the PL excitation spectrum shows transitions that are forbidden in the absence of an electric field and the emergence of new energy levels confined by the tilted barrier in the hole bands.
InGaAs SQWs grown on GaAs (111)A-oriented substrates show strain relaxation even for layers below the predicted critical thickness. A strain relaxation mechanism peculiar to this surface was found. We made pin diodes with SQWs grown on GaAs (111)A゜5 off-oriented substrates. The PL spectrum shows the influence of the piezoelectric field. We demonstrate the blueshift of the PL peaks with applied bias and propose a bistable device using this effect.
Finally, temporal variations of the PL peak wavelength due to screening of the piezoelectric field by photogenerated carriers were studied in undoped samples by using time-resolved and wavelength-resolved measurements of the PL intensity decay. The partial screening of the piezoelectric field by photo generated carriers shifts the PL peak to shorter wavelengths and increases the oscillator strength. Results are explained using a model based on rate equations of photogenerated carriers and a recombination probability which is a function of the screened electric field.
KEYWORDS: InGaAs, (111)A, (211)A, (311)A, (411)A, substrate orientation, strained layer, photoluminescence, quantum well, piezoelectricity, molecular beam epitaxy.