Observation of room temperature optical absorption in InP/GaAs type-II ultrathin quantum wells and quantum dots

Abstract

Room temperature optical absorption process is observed in ultrathin quantum wells (QWs) and quantum dots (QDs) of InP/GaAs type-II band alignment system using surface photovoltage spectroscopy technique, where no measurable photoluminescence signal is available. Clear signature of absorption edge in the sub band gap region of GaAs barrier layer is observed for the ultrathin QWs and QDs, which red shifts with the amount of deposited InP material. Movement of photogenerated holes towards the sample surface is proposed to be the main mechanism for the generation of surface photovoltage in type-II ultrathin QWs and QDs. QDs of smaller size are found to be free from the dislocations as confirmed by the high resolution transmission electron microscopy images.

Surface photovoltage spectroscopy of an epitaxial ZnO/GaP heterojunction

“…Information on theelectronic transitions can be obtained even in the case where thedeposited layer has alarger band gap as compared to that of the substrate [18]. The SPS technique cannot only provide information on electronic transitions for thin films [18,19], but also onlow dimensional semiconductors like quantum wells (QWs) [20], quantum dots [21,22] and even ultrathin QWs having width in the range of 0.7 to 2.14 monolayers [20,23,24]. However, very few reports are availablewhere SPS measurements are used to extract information related to the electronic transitions for ZnO layers [25,26].…”