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An extensive study has been conducted on a series of AlGaN/GaN high electron mobility transistor (HEMT) samples using metalorganic vapour phase epitaxy, to investigate the influence of growth modes for GaN buffer layers on device performance. The unintentional doping concentration and screw dislocation density are significantly lower in the samples grown with our special two-dimensional (2D) growth approach, compared to a widely-used two-step method combining the 2D and 3D growth. The GaN buffer layers grown by the 2D growth approach have achieved an unintentional doping density of 2 × 1014 cm−3, two orders lower than 1016 cm−3 of the GaN samples grown using a conventional two-step method. High-frequency capacitance measurements show that the samples with lower unintentional doping densities have lower buffer leakage and higher breakdown limits. This series of samples have attained sub-nA/mm leakages, a high breakdown limit of 2.5 MV/cm, and a saturation current density of about 1.1 A/mm. It indicates that our special 2D growth approach can effectively lessen the unintentional doping in GaN buffer layers, leading to low buffer leakage and high breakdown limits of GaN/AlGaN HEMTs. [ABSTRACT FROM AUTHOR]

A systematic study has been conducted on a series of InGaN‐based micro‐light‐emitting diode (μLED) array samples which are achieved using the direct epitaxy overgrown approach on patterned templates by metalorganic chemical vapor deposition technique, where the diameters of the μLEDs are 40, 5, and 3.6 μm, respectively. The selective epitaxy approach allows to circumvent the major limitations of conventional fabrication methods of μLEDs which unavoidably introduce dry‐etching‐induced damages. Electrical characterizations are performed on the selective epitaxy overgrown μLEDs as well as conventional μLEDs fabricated using a standard dry‐etching method. For the overgrown μLEDs, the leakage current per μLED is smaller than those of the conventionally mesa‐etched μLEDs. It is worth highlighting that the single 3.6 μm μLED exhibits as low as a leakage current of 14.1 nA at a bias of −5 V. Moreover, in terms of leakage current density, the overgrown μLEDs exhibit much smaller and more consistent leakage than their mesa‐etched counterparts. Operational voltage RC constants also show more favorable to the overgrown devices than the conventionally mesa‐etched μLEDs. [ABSTRACT FROM AUTHOR]

There is a significantly increasing demand on developing a microLED (μLED) based microdisplay which may be the only display system that can meet the requirements for augmented reality/virtual reality systems, helmet mounted displays, and head‐up displays. However, a number of fundamental challenges which cannot be met by any existing technologies need to be overcome before such a microdisplay with satisfied performance becomes possible. In this paper, a different type of integration concept using an epitaxial approach is proposed, aiming to monolithically integrate μLEDs and high electron mobility transistors (HEMTs) on a single chip. This concept can be potentially realized by using a selective epitaxial overgrowth method on a predefined HEMT template featuring microhole masks. Finally, the proposed epitaxial integration concept is translated into a prototype, demonstrating an 8 × 8 microLED microdisplay, where each μLED is electrically driven by an individual HEMT which surrounds its respective μLED via the gate bias of the HEMT. [ABSTRACT FROM AUTHOR]

High‐quality semi‐polar (11‐22) GaN is obtained by means of growth on patterned (113) silicon substrates featured with stripy grooves and extra periodic gaps which are perpendicular to the grooves. Ga melting‐back during the GaN growth at a high temperature is eliminated as a result of special patterning design. On‐axis X‐ray rocking curve measurements show that the linewidth is significantly reduced down to 339 arcsec. Photoluminescence (PL) measurements at 10 K show strong GaN band‐edge emission only, meaning that any basal stacking fault‐related emission is not observed. Furthermore, green InGaN/GaN light‐emitting diodes (LEDs) with an emission wavelength of around 530 nm are achieved on the semi‐polar GaN grown on the patterned Si substrates. Excitation power‐dependent PL measurements do not show a shift in wavelength, meaning a significant reduction in polarization‐induced piezoelectric fields. Electroluminescence (EL) measurements exhibit that the output power of the semi‐polar LED increases linearly with increasing injection current. It is worth highlighting that the overgrowth technology on designed patterned (113) silicon is a potential approach to manufacturing high‐performance semi‐polar GaN emitters on Si substrates in a long wavelength region. [ABSTRACT FROM AUTHOR]