UC Santa Barbara

Although MOCVD is regarded as the preferred growth method for commercial grade nitride-based semiconductor devices, there are still certain applications for which MBE may be utilized. Current record-performing N-polar HEMTs are grown by MOCVD which must use miscut SiC and sapphire substrates. The growth conditions employed by MBE, however, enable growth of N-polar GaN on non-vicinal substrates. MOCVD grown GaN-on-SiC N-polar HEMTs typically have a threading dislocation density on the order of 108 cm-2. Amplifiers biased in class-A mode operate at a high source-to-drain quiescent current. High current in a material with a high density of scattering centers (such as dislocations) may lead to power dissipation in the form of heat which can impede device efficiency. MBE grown N-polar HEMT epi-structures on low dislocation density bulk GaN substrates may improve this efficiency. Furthermore, the low temperature growth used by MBE enables thicker coherently strained AlN interlayers, or back-barriers, which can mitigate the effects of alloy scattering in the 2DEG channel. Although N-polar GaN grown on bulk GaN by MBE typically results in a surface riddled with V-defects, this work demonstrates suppression of V-defects by initiating growth with just 2 nm of AlN. It was shown that the generation of these pits may be attributed to impurities on the regrowth interface. InGaN grown by MBE has the advantage of growing thick layers without generating V-defects on the surface. Furthermore, the lower growth temperatures employed by MBE enable extremely high In-mole fraction InGaN. This is advantageous for growing thick, relaxed InGaN on compliant substrates for long-wavelength nitride-based optoelectronics. The simplicity of MBE, which does not use any metal-organic precursors or carrier gases, makes it suitable for proof-of-concept next generation devices. Composition pulling and Quantum Confined Stark Effect (QCSE) has severely limited nitride-based red LEDs to achieve the efficiencies shared by their blue and green counterparts. MOCVD grown elastically relaxed InGaN on porous GaN tiles have shown significant progress however they are limited due to the high density of V-defects on the surface. This work demonstrates MBE grown InGaN on porous GaN tiles with a surface free of V-defects which had an in-plane lattice constant equivalent to fully relaxed In0.12Ga0.88N. STEM analysis revealed no new dislocations in the InGaN layer demonstrating the compliant nature of the porous tile. This is a significant improvement from previous work by MOCVD. These MBE grown tiled pseudo-substrates may be a compelling technology for micro-LED displays.