Differential photo-voltage spectroscopy for characterizing epitaxial multilayered and quantum well structures

Abstract

An improved photo-voltage spectroscopy (PVS) technique, capable of accurately characterizing multilayered and quantum well structures, is presented. The technique is developed by noise reduction and differentiation of the photovoltage signal which improves the accuracy and sensitivity of the standard photo-voltage spectroscopy dramatically. The resulting differential-photo-voltage spectroscopy is capable of measuring the energy gap (Eg) and hence the composition, of ternary and quaternary compounds in multilayered structures at room temperature, with a substantially higher degree of confidence than the standard PVS technique. Several structures have been examined successfully. Two representative AlGaAs/GaAs structures are reported here to establish the capabilities of this technique. These structures were found to provide values for Eg and Al mole fraction, in excellent agreement with both the targeted values based on reflective high-energy electron diffraction oscillations during molecular beam epitaxial growth, and the measured values from variable angle ellipsometry. Numerous exciton transitions from quantum wells are clearly resolved and shown to be in excellent agreement with the theoretically predicted ones.