Two dimensional electron gas in a hybrid GaN/InGaN/ZnO heterostructure with ultrathin InGaN channel layer G. Atmaca n , P. Narin, B. Sarikavak-Lisesivdin, S.B. Lisesivdin Gazi University, Faculty of Science, Department of Physics, 06500 Teknikokullar, Ankara, Turkey HIGHLIGHTS  We calculated 2DEG properties for hybrid GaN/In x Ga 1x N/ZnO HEMT structures.  This paper shows that 2DEG density of these structures can reach over 1  10 13 cm 2 .  We investigated effects of ultrathin InGaN channel layer on 2DEG of these structures.  We propose an optimized device structure to reduced short channel effects. article info Article history: Received 5 June 2015 Received in revised form 7 December 2015 Accepted 11 December 2015 Available online 13 December 2015 Keywords: InGaN GaN ZnO 2DEG Short-channel effects abstract We investigated the influence of an ultrathin InGaN channel layer on two-dimensional electron gas (2DEG) properties in a newly proposed hybrid GaN/In x Ga 1x N/ZnO heterostructure using numerical methods. We found that 2DEG carriers were confined at InGaN/ZnO and GaN/InGaN interfaces. Our calculations show that the probability densities of 2DEG carriers at these interfaces are highly influenced by the In mole fraction of the InGaN channel layer. Therefore, 2DEG carrier confinement can be ad- justable by using the In mole fraction of the InGaN channel layer. The influence of an ultrathin InGaN channel layer on 2DEG carrier mobility is also discussed. Usage of an ultrathin InGaN channel layer with a low indium mole fraction in these heterostructures can help to reduce the short-channel effects by improvements such as providing 2DEG with higher sheet carrier density which is close to the surface and has better carrier confinement. & 2015 Elsevier B.V. All rights reserved. 1. Introduction In recent years, III–V and II–VI group semiconductor material systems have been studied as hybrid heterostructures for light- emitting diodes (LEDs) applications [1–3]. In addition to widely studied AlGaN/GaN, InGaN/GaN systems, hybrid ZnO/InGaN/GaN [4], InGaN/MgZnO [5], InGaN/CdZnO [6], p-GaN/InGaN/ZnO [7] heterostructures for LED applications and hybrid n-ZnO/i-InGaN/ p-GaN [8] heterostructures for solar cell applications have been also studied in a number of studies. In 2010, dc characteristics of GaN/InGaN/ZnO npn heterojunction bipolar transistors were also examined by K. Hsueh et al. [9]. Furthermore, without any doping, GaN and ZnO based hybrid heterostructures may be an alternative material system for high electron mobility transistor (HEMT) ap- plications due to their spontaneous and piezoelectric polarization properties. Strong piezoelectric polarization (P PE ) and spontaneous polarization ( P SP ) between GaN and ZnO ( = − P 0.034 GaN SP C/m 2 , = − P 0.050 ZnO SP C/m 2 ) can lead to high induced sheet carrier densities within two-dimensional electron gas (2DEG) at an in- terface of the related hybrid heterostructure [10–12]. On the other hand, similar material properties of GaN and ZnO such as room temperature band gaps, electron drift velocities and wurtzite crystal structures are promising for building up GaN and ZnO based hybrid transistor heterostructures [4,12,13]. For GaN epi- taxial layers grows, ZnO substrates can be a successor to widely used sapphire substrates. ZnO has a common stacking order with GaN, and there is low lattice mismatch between ZnO and GaN (about 2%) [14,15], which also very low when compared with the lattice mismatch between sapphire and GaN (about %14). ZnO can be grown at low temperatures compared with GaN growth [8]. This is important due to the stability problems of indium atoms at high temperatures in InGaN epitaxial layer growths [8,16]. The development of GaN epitaxial layer growth using a ZnO buffer offers a significant advantage for future studies of hybrid GaN and ZnO based heterostructures [15]. In a GaN-based transistor heterostructure, the 2DEG channel Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E http://dx.doi.org/10.1016/j.physe.2015.12.010 1386-9477/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: gokhanatmaca@kuark.org (G. Atmaca). Physica E 79 (2016) 67–71