Epitaxial Growth of InAlN/GaN Heterostructures on Silicon Substrates in a Single Wafer Rotating Disk MOCVD Reactor
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Epitaxial Growth of InAlN/GaN Heterostructures on Silicon Substrates in a Single Wafer Rotating Disk MOCVD Reactor Jing Lu, Jie Su, Ronald Arif, George D. Papasouliotis, and Ajit Paranjpe Veeco MOCVD Operations, 394 Elizabeth Avenue, Somerset, NJ 08873, USA. ABSTRACT InAlN films and InAlN/GaN high electron mobility transistor (HEMT) structures were demonstrated on 150mm Si using Veeco's Propel single wafer metal-organic chemical vapor deposition (MOCVD) system. Smooth surfaces with root mean square (rms) roughness of 0.68 nm were observed in a 5x5 μm2 atomic force microscope (AFM) scan. X-ray diffraction (XRD) analysis shows well-defined layer peaks and fringes, indicating good structural quality and abrupt layer interfaces. Thickness uniformity of InAlN is 0.87%, 1ı, for a 7-point XRD measurement across the 150 mm wafer. Secondary ion mass spectrometry (SIMS) analysis confirms the uniform indium depth profile and the presence of abrupt layer interfaces. Negligible Ga (< 100 ppm, atomic) incorporation was detected in the InAlN bulk film. Film sheet resistance of 230ȍ/sq , charge of 2.1×1013/cm2, and mobility of 1270 cm2/V.s were measured on a prototypical InAlN/GaN HEMT structure comprising a 10 nm-thick, 17% indium, InAlN barrier. INTRODUCTION Even though the majority of development efforts for high power and high frequency applications have focused on AlGaN/GaN HEMTs, InxAl1-xN shows promise as a candidate material for the gate barrier and polarization charge-inducing layer because of its wide bandgap, high spontaneous polarization charge, and lattice-matching to GaN [1]. However, the growth of InAlN by MOCVD is challenging as the optimal conditions for AlN and InN growth are substantially different, and potential incorporation of Ga into the film compromises the sharp interfaces required in HEMT structures encompassing InAlN. Many researchers have observed the unintentional incorporation of Ga in the InAlN layer grown by MOCVD [2-4]. The unintentional Ga incorporation effect makes it difficult to control the film composition and growth repeatability. The parasitic formation of a GaN-rich layer at the InAlN/AlN interface can degrade both two-dimensional electron gas (2DEG) density and mobility of the heterojunctions [5]. Epitaxial growth on large diameter silicon substrates has enabled both reduction in manufacturing cost and potential integration with Si-based CMOS technologies [6-8]. MOCVD growth of high quality epitaxy of InAlN/GaN HEMTs on large diameter silicon substrates is of great interest for power and high frequency applications. EXPERIMENT InAlN films and InAlN/GaN HEMT structures were epitaxially grown on 150 mm Si, using Veeco's Propel single wafer MOCVD system (Figure 1(a)). The Turbodisc, vertical rotating disk reactor encompasses the core reaction and high velocity laminar flow characteristics of its predecessor batch systems, thus enabling stable, repeatable operation, long preventive maintenance cycles, and direct, model-based process scale up. Moreover, it incorporates
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