Characterization of a graded index of refraction separate confinement heterostructure (GRINSCH) laser structure using contactless electroreflectance

Using contactless electroreflectance we have characterized the complete potential profile of a pseudomorphic 0.98 μm InGaAs/GaAs/GaAlAs graded index of refraction separate confinement heterostructure (GRINSCH) laser fabricated by molecular beam epitaxy. Signals were detected from all three relevant portions of the sample. Comparison of the observed transitions from the InGaAs single quantum well (SQW) section with an envelope function calculation (including the effects of strain and electric field) made it possible to evaluate the In composition and width of the SQW. These values are in good agreement with the intended parameters. The energy of 11HH, the fundamental conduction to heavy-hole level (which is closely related to the lasing frequency) can easily be determined to less than ±1 meV at 300 K. From the period of the observed Franz–Keldysh oscillations (FKOs) originating in the GaAlAs GRINSCH region it was possible to directly evaluate the built-in electric field in the structure. We also present a general expression for FKOs in the presence of both electric fields (due to charge) and the “fields” (potential gradient) due to compositional grading. The temperature dependence (20 K