Abstract
In this work, we report on the innovative growth of semipolar “bow-tie”-shaped GaN structures containing InGaN/GaN multiple quantum wells (MQWs) and their structural and luminescence characterization. We investigate the impact of growth on patterned (113) Si substrates, which results in the bow-tie cross section with upper surfaces having the (101¯1) orientation. Room temperature cathodoluminescence (CL) hyperspectral imaging reveals two types of extended defects: black spots appearing in intensity images of the GaN near band edge emission and dark lines running parallel in the direction of the Si stripes in MQW intensity images. Electron channeling contrast imaging (ECCI) identifies the black spots as threading dislocations propagating to the inclined (101¯1) surfaces. Line defects in ECCI, propagating in the [12¯10] direction parallel to the Si stripes, are attributed to misfit dislocations (MDs) introduced by glide in the basal (0001) planes at the interfaces of the MQW structure. Identification of these line defects as MDs within the MQWs is only possible because they are revealed as dark lines in the MQW CL intensity images, but not in the GaN intensity images. Low temperature CL spectra exhibit additional emission lines at energies below the GaN bound exciton emission line. These emission lines only appear at the edge or the center of the structures where two (0001) growth fronts meet and coalesce (join of the bow-tie). They are most likely related to basal-plane or prismatic stacking faults or partial dislocations at the GaN/Si interface and the coalescence region.
Highlights
Over half a century ago, silicon revolutionized the semiconductor industry through its use in transistors and integrated circuits.1,2 Decades later, it may be said that another revolution occurred, but this time in the field of solid-state lighting, through the advances of III-nitride semiconductors and their applications in light-emitting diodes (LEDs) and high power transistors.3Commercial nitride optoelectronic devices are commonly grown on sapphire substrates along the polar c-direction
GaN was grown by metal-organic chemical vapor deposition (MOCVD) on (113) Si substrates, which had been patterned into periodic stripes to expose f111g sidewalls
Growth of (0001)-orientated GaN from opposing f111g Si surfaces led to the formation of GaN structures with “bow-tie” shaped cross-section and two inclined (1011) top surface facets with InGaN/GaN multiple quantum wells (MQWs) grown on top
Summary
Over half a century ago, silicon revolutionized the semiconductor industry through its use in transistors and integrated circuits. Decades later, it may be said that another revolution occurred, but this time in the field of solid-state lighting, through the advances of III-nitride semiconductors and their applications in light-emitting diodes (LEDs) and high power transistors.. At the usual GaN growth temperatures, Ga strongly reacts with Si forming a eutectic alloy.11 This causes strong etching of the material, referred to as “melt-back etching.” In addition to the lattice mismatch, another major issue is the mismatch in thermal expansion coefficients (%46%) between GaN and Si. This causes strong etching of the material, referred to as “melt-back etching.” In addition to the lattice mismatch, another major issue is the mismatch in thermal expansion coefficients (%46%) between GaN and Si They both produce tensile strain, leading to wafer cracking and bowing, which is more pronounced compared with sapphire substrates.. The cross-sectional bow-tie shape, as seen, is due to the patterning of the Si substrate and the subsequent growth of GaN on the f111g family of planes of Si. Cathodoluminescence (CL) hyperspectral imaging shows areas of nonradiative recombination associated with extended defects at room temperature and emission lines related to stacking faults at low temperature. These defects, giving rise to nonradiative recombination at room temperature, were identified as threading dislocations (TDs) and misfit dislocations (MDs) using electron channeling contrast imaging (ECCI)
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