Single crystalline nanomembranes (NMs) represent a new embodiment of semiconductors having a two-dimensional flexural character with comparable crystalline perfection and optoelectronic efficacy. In this Letter, we demonstrate the preparation of GaN NMs with a freestanding thickness between 90 to 300 nm. Large-area (>5 × 5 mm(2)) GaN NMs can be routinely obtained using a procedure of conductivity-selective electrochemical etching. GaN NM is atomically flat and possesses an optical quality similar to that from bulk GaN. A light-emitting optical heterostructure NM consisting of p-GaN/InGaN quantum wells/GaN is prepared by epitaxy, undercutting etching, and layer transfer. Bright blue light emission from this heterostructure validates the concept of NM-based optoelectronics and points to potentials in flexible applications and heterogeneous integration.

Red-green-blue (RGB) full-color micro light-emitting diodes (μ-LEDs) fabricated from semipolar (20-21) wafers, with a quantum-dot photoresist color-conversion layer, were demonstrated. The semipolar (20-21) InGaN/GaN μ-LEDs were fabricated on large (4 in.) patterned sapphire substrates by orientation-controlled epitaxy. The semipolar μ-LEDs showed a 3.2 nm peak wavelength shift and a 14.7% efficiency droop under 200    A / cm 2 injected current density, indicating significant amelioration of the quantum-confined Stark effect. Because of the semipolar μ-LEDs’ emission-wavelength stability, the RGB pixel showed little color shift with current density and achieved a wide color gamut (114.4% NTSC space and 85.4% Rec. 2020).

The light-emitting diode (LED) is among promising candidates of light sources in visible light communication (VLC); however, strong internal polarization fields in common c-plane LEDs, especially green LEDs, result in low frequency and limited transmission performance. This study aims to overcome the limited 3-dB bandwidth of long-wavelength InGaN/GaN LEDs. Thus, semipolar (20–21) micro-LEDs (μLEDs) were fabricated through several improved approaches on epitaxy and chip processes. The μLED exhibits a 525 nm peak wavelength and good polarization performance. The highest 3-dB bandwidth up to 756 MHz and 1.5 Gbit/s data rate was achieved under a current density of 2.0 kA/cm2. These results suggest a good transmission capacity of green semipolar (20–21) μLEDs in VLC applications.

Here, we demonstrate a process to produce planar semipolar (202¯1) GaN templates on sapphire substrates. We obtain (202¯1) oriented GaN by inclined c-plane sidewall growth from etched sapphire, resulting in single crystal material with on-axis x-ray diffraction linewidth below 200 arc sec. The surface, composed of (101¯1) and (101¯0) facets, is planarized by the chemical-mechanical polishing of full 2 in. wafers, with a final surface root mean square roughness of <0.5 nm. We then analyze facet formation and roughening mechanisms on the (202¯1) surface and establish a growth condition in N2 carrier gas to maintain a planar surface for further device layer growth. Finally, the capability of these semipolar (202¯1) GaN templates to produce high quality device structures is verified by the growth and characterization of InGaN/GaN multiple quantum well structures. It is expected that the methods shown here can enable the benefits of using semipolar orientations in a scalable and practical process and can be readily extended to achieve devices on surfaces using any orientation of semipolar GaN on sapphire.

Epitaxial lateral overgrowth (ELO) of nitrogen-polar (0001̅ ) GaN (N-polar GaN) by metalorganic vapor deposition has been studied to achieve a high microstructural quality of N-polar GaN. The influence of growth conditions on lateral growth is investigated, and a correlation of growth conditions with the observed inversion of polarity is established. Most of the observed trends for N-polar ELO are contrary to those reported for Ga-polar experiments. Such differences are explained by considering the property of surface reactivity of N-polar GaN with hydrogen species. On the basis of the trends of the occurrence (or absence) of polarity inversion, an atomistic model is proposed to explain the origin of polarity inversion. This model also allows us to control the process and to completely eliminate polarity inversion, resulting in fully coalesced, purely Npolar GaN with improved crystalline quality.