The influence of Al content on impurity states in GaN/AlGaN asymmetrically coupled quantum dots

Abstract

We present a calculation of the donor impurity states in zincblende (ZB) GaN/AlGaN asymmetrically coupled quantum dots (ACQDs). Numerical results show that the donor binding energy is distributed asymmetrically with respect to the center of the ACQDs for any Al composition. It is also found that for an impurity located inside a wide dot, the donor binding energy is insensitive to the middle barrier width (L mb ! 3 nm) in ZB GaN/Al 0.15 Ga 0.85 N ACQDs. However, for an impurity located inside a narrow dot, the donor binding energy has a minimum value with increasing Al composition. 1 Introduction GaN-based quantum dots (QDs) have attracted much attention as promising candidates for application in optical, optoelectronic, and electronic devices [1][2][3]. It is well known that the wide-band-gap nitride has both wurtzite (WZ) and zinc-blende (ZB) structure phases. Very recently, compared with WZ GaN-based heterostructures, the absence of the built-in electric field is one of the distinguishing physical properties of ZB GaN-based quantum heterostructures [4][5][6][7]. In addition, there is also an increasing interest in ZB GaN QDs due to the improvement that occurs in their growth processes to take advantage of higher saturated electron-drift velocity, easily cleaved cavities for laser diodes and lower band energy in technological applications [8,9]. So, ZB GaN-based quantum structures are expected to have many advantages in optoelectronic devices.It is well known that impurity states play a very important role in semiconductor optoelectronic devices. A deep understanding of the effects of impurities on electronic states of semiconductor heterostructures is a fundamental question in semiconductor physics because their presence can dramatically alter the performance of quantum devices [10]. In the past, much theoretical and experimental work has been devoted in investigating the electronic states in different shape QDs [11][12][13][14][15]. These studies show that the binding energy of hydrogenic impurities in semiconductor heterostructures depends upon material, geometry, and