Photoreflectance Study of Modulation-Doped GaAs/GaAlAs Quantum Dots Fabricated by Reactive-Ion Etching

Abstract

AbstractUsing contactless photoreflectance at 300K and 77K we have investigated the intersubband transitions from two modulation-doped GaAs/GaAlAs quantum dot (QD) arrays fabricated by reactive-ion etching (RIE). The samples consisted of 8 nm decoupled GaAs/GaAlAs quantum wells with dot sizes (lateral dimensions) of 60 and 100 nm. The lineshapes of the “IC-IH” and “IC-IL” features were indicative of a screened exciton, i.e., the derivative of a broadened twodimensional density of states (step function), due to the presence of the electron gas. On the other hand, even at 300K the “2C-2H“ features exhibited a well-defined sharp excitonic lineshape, i.e., derivative of a Gaussian profile. Even at room temperature it is possible to detect the effects of the lateral quantum confinement. We have observed a 2 meV blue shift of the “2C-2H” feature of the 60 nm QD array in relation to the 100 nm QD array. At 77K we have found evidence for a “parabolic-like” in-plane confining potential on the smaller QD array. This experiment demonstrates the considerable utility of PR in studying these reduced dimensional systems.