DIFFERENTIAL PHOTO-VOLTAGE SPECTROSCOPY FOR CHARACTERIZING EPITAXIAL MULTILAYERED AND QUANTUM-WELL STRUCTURES

An improved photo-voltage spectroscopy (PVS) technique, capable of acc urately characterizing multilayered and quantum well structures, is pr esented. The technique is developed by noise reduction and differentia tion of the photovoltage signal which improves the accuracy and sensit ivity of the standard photo-volt age spectroscopy dramatic ally. The r esulting differential-photo-voltage spectroscopy is capable of measuri ng the energy gap (E(g)) and hence the composition, of ternary and qua ternary compounds in multilayered structures at room temperature, with a substantially higher degree of confidence than the standard PVS tec hnique. Several structures have been examined successfully. Two repres entative AlGaAs/GaAs structures are reported here to establish the cap abilities of this technique. These structures were found to provide va lues for E(g) and Al mole fraction, in excellent agreement with both t he targeted values based on reflective high-energy electron diffractio n oscillations during molecular beam epitaxial growth, and the measure d values from variable angle ellipsometry. Numerous exciton transition s from quantum wells are clearly resolved and shown to be in excellent agreement with the theoretically predicted ones.