Electroreflectance of GaAs-AlGaAs modulation-doped field-effect transistors.

We report the measurements of changes in the reflectivity spectrum of GaAs-AlGaAs modulation-doped field-effect transistors near the band gaps of both materials when a gate voltage is applied to vary the charge density at the interface. The observed changes (up to 0.3% at the band edge of AlGaAs) are attributed to the high external fields (˜10[sup 5] V/cm) which modulate the already existing band bending, leading to changes in the band-edge absorption due to FranzKeldysh effects in the quantum-confined structures. The possibility of using the effect for optical readout of transistor action is discussed. [ABSTRACT FROM AUTHOR]