Growth temperature - phase stability relation in In 1-x Ga x N epilayers grown by high-pressure CVD
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1202-I05-21
Growth temperature - phase stability relation in In1-xGaxN epilayers grown by highpressure CVD
G. Durkaya1, M. Alevli1, M. Buegler1,2, R. Atalay1, S. Gamage1, M. Kaiser2, R. Kirste2, A. Hoffmann2, M. Jamil3, I. Ferguson3 and N. Dietz1 1 Department of Physics & Astronomy, Georgia State University, Atlanta, GA 30303 2 Technical University Berlin, Institute of Solid State Physics, Berlin, Germany 3 School of ECE, University of North Carolina at Charlotte, Charlotte, NC 28223 ABSTRACT The influence of the growth temperature on the phase stability and composition of singlephase In1-xGaxN epilayers has been studied. The In1-xGaxN epilayers were grown by high-pressure Chemical Vapor Deposition with nominally composition of x = 0.6 at a reactor pressure of 15 bar at various growth temperatures. The layers were analyzed by x-ray diffraction, optical transmission spectroscopy, atomic force microscopy, and Raman spectroscopy. The results showed that a growth temperature of 925 °C led to the best single phase InGaN layers with the smoothest surface and smallest grain areas. INTRODUCTION The ternary In1-xGaxN alloy system attracts significant attention due to its unique physical properties such as direct band-gap, high carrier mobility, and strong chemical bonding[1,2]. The optical band gap of the In1-xGaxN alloy system can be tuned from ultraviolet (EgGaN=3.4 eV) to near-infrared (EgInN=0.7eV), spanning over more than 80% of the solar spectrum. This is of interest for the development of high-efficiency monolithic multijunction photovoltaic solar cells based on In1-xGaxN / Ga1-xInxN heterostructures. However, the growth of the In1-xGaxN alloys and heterostructures is a challenge due to the lower disassociation temperature of InN compared to that of GaN. A further challenge is the large difference between the lattice constants of the binaries InN and GaN[3] (~11%), which may induce lattice strain[4] and contribute to a potential solid-phase miscibility gap in the ternary In1-xGaxN system[5]. These facts contribute to the reported compositional inhomogeneity observed in InGaN layers[6-11], which reduces the device efficiencies of InGaN based optoelectronic structures. The phase stability of InGaN epilayers has been studied for different growth temperatures with different growth techniques[7,10,11]. For instance, InGaN layers grown by RF-MBE show a linear correlation between gallium incorporationwith increased growth temperature between 600°C - 700°C[10]. MOVPE grown InGaN layers exhibited a similar behavior in the temperature range between 700°C - 850°C[12]. Pantha et al.[7] reported the growth of single phase InGaN layers by MOCVD and observed a decreased indium incorporation with increasing growth temperature from 600°C - 750°C. This research effort explores the potential of highpressure Chemical Vapor Deposition (HPCVD) to improve the phase stability in InGaN layers, utilizing high pressures nitrogen gas to stabilize the In1-xGaxN growth surface and effectively suppressing the thermal decomposition process above t
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