Influence of Growth Conditions on Phase Separation of InGaN Bulk Material Grown by MOCVD
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0955-I07-20
Influence of Growth Conditions on Phase Separation of InGaN Bulk Material Grown by MOCVD Yong Huang, Omkar Jani, Eun Hyun Park, and Ian Ferguson School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, 30332 ABSTRACT: Different types of phase separation in thick InGaN layers were studied using photoluminescence (PL) and x-ray diffraction (XRD). InGaN films of 100 nm in thickness were grown on 2 µm GaN templates with an In molar fraction ranging from 0% to 20% by metal organic chemical phase deposition (MOCVD). It is shown that suppression of the phase separation in InGaN can be made possible by increasing the TMIn flow rate, decreasing the layer thickness and decreasing the growth rate. Based on the results, two types of phase separation, microscopic quantum dots and macroscopic domains, are proposed accordingly. The influence of the growth conditions on each type is summarized respectively in this paper.
INTRODUCTION The band gaps of InGaN alloy cover a wide spectral range from near infra-red (InN) to UV (GaN), and InGaN alloys are widely used as the active layer in light-emitting devices. Moreover, the revised bandgap value of InN has been attracting attention due to the possibility of fabricating solar cells based solely on nitride materials. Wide bandgap InGaN alloys can also be used as a high energy window for high performance solar cells. Growth of InGaN alloys has proven to be extremely challenging. A trade-off has to be made between the epilayers quality and amount of indium incorporated. Moreover, theoretical calculation points out large miscibility gap between InN and GaN based on thermodynamics [1]. In reality, the phase separation could be more kinetically driven on the surface, especially during the growth of MOCVD or molecular beam epitaxy (MBE). Different growth parameters may have different impact on the phase separation, which is studied in this paper. EXPERIMENTAL DETAILS The growth was performed in an Emcore MOCVD D-125 rotating disk reactor with a short jar configuration. Initially, about two micron thick GaN templates were grown on (0001) sapphire at 1020 oC using trimethyl gallium (TMGa) and ammonia (NH3) as the gallium and nitrogen sources, respectively. Subsequently, temperature was lowered to 600 to 800 oC, and carrier gas was switched from H2 to N2. InGaN films of about 100 nm thick with varying indium concentration were grown by introducing trimethyl indium (TMIn), triethyl gallium (TEGa) and NH3 into the reactor. The growth procedure was monitored using optical reflectometry. Crystalline quality and indium composition were examined by high-resolution XRD using a Philips X’Pert Pro MRD diffractometer. Atomic force microscopy (AFM) was performed using a PSIA XE-100. Room temperature PL was excited by a He-Cd laser at 325 nm.
RESULTS AND DISCUSSION The indium composition, as determined by XRD, ranges from 0% to 20% depending on the growth conditions. At 720 oC with 30 sccm TEGa, high-quality InGaN layers with 7% indium can be repeatedly obt
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