DETERMINING ENERGY-BAND OFFSETS IN QUANTUM-WELLS USING ONLY SPECTROSCOPIC DATA

We have developed an experimental technique for accurately determining energy-band offsets in semiconductor quantum wells (QW) based on the fact that the magnitude of the ground-state light-hole (LH) energy is more sensitive to the depth of the valence-band well than is the ground-state heavy-hole (HH) energy. In a lattice-matched, unstrained QW system, this behavior causes the energy difference between the LH and HH excitons to go through a maximum as the well width, L(z), increases from zero. Calculations show that the position, and more importantly, the magnitude of this maximum is a sensitive function of the valence-band offset, Q(v), the parameter which determines the depth of the valence-band well. By using Q(v), or alternatively Q(c)=1-Q(v), as an adjustable parameter and fitting experimentally measured LH-HH splittings as a function of L(z), an accurate determination of band offsets can be derived. However, we further reduce the experimental uncertainty by plotting LH-HH as a function of HH energy (which is, itself, a function of L(z)) rather than L(z), since then all of the relevant data values can be precisely determined from absorption spectroscopy alone. Using this technique, we have derived the conduction-band offsets for several material systems, including lattice-mismatched systems and, where a consensus has developed, have obtained values in good agreement with other determinations.