Topical Review: Development of overgrown semi-polar GaN for high efficiency green/yellow emission

Abstract

The most successful example of large lattice-mismatched epitaxial growth of semiconductors is the growth of III-nitrides on sapphire, leading to the award of the Nobel Prize in 2014 and great success in developing InGaN-based blue emitters. However, the majority of achievements in the field of III-nitride optoelectronics are mainly limited to polar GaN grown on c-plane (0001) sapphire. This polar orientation poses a number of fundamental issues, such as reduced quantum efficiency, efficiency droop, green and yellow gap in wavelength coverage, etc. To date, it is still a great challenge to develop longer wavelength devices such as green and yellow emitters. One clear way forward would be to grow III-nitride device structures along a semi-/non-polar direction, in particular, a semi-polar orientation, which potentially leads to both enhanced indium incorporation into GaN and reduced quantum confined Stark effects. This review presents recent progress on developing semi-polar GaN overgrowth technologies on sapphire or Si substrates, the two kinds of major substrates which are cost-effective and thus industry-compatible, and also demonstrates the latest achievements on electrically injected InGaN emitters with long emission wavelengths up to and including amber on overgrown semi-polar GaN. Finally, this review presents a summary and outlook on further developments for semi-polar GaN based optoelectronics.

Semipolar GaN(10–11) Epitaxial Layer Prepared on Nano‐Patterned SiC/Si(100) Template

“…However, application in optoelectronic devices of the GaN (0001) plane results in the Stark effect appearance due to strong piezoelectric polarization. Nowadays, to avoid detrimental influence of the Stark effect, the optoelectronic devices are formed on the basis of non‐polar or semipolar GaN structures . Among different substrate materials as Al 2 O 3 , SiC, and Si used for heteroepitaxy of III–nitride structures, silicon is the most attractive one.…”

Microstructure investigation of semi-polar (11-22) GaN overgrown on differently designed micro-rod array templates

“…The current status of the development of (11-22) GaN on sapphire can be referred to a topical review published very recently. 1 In comparison with the (0001) polar orientation, InGaN/GaN based emitters grown along the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) direction are subjected to significantly reduced piezoelectric polarization fields, thus effectively increasing their internal quantum efficiency (IQE) by reducing the associated quantum confined stark effect (QCSE). [2][3][4] Furthermore, the (11-22) plane has been predicted to exhibit a lower indium chemical potential than either non-polar or polar surfaces, 5 making (11-22) GaN accommodate indium atoms more easily than either nonpolar or polar GaN.…”

“…So far, all the semi-polar III-nitride laser structures have been grown exclusively on extremely expensive free-standing semi-polar GaN substrates. 1,8,9 Therefore, it implies that it is necessary to further improve the crystal quality of any overgrown (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)) GaN on sapphire in order to achieving lasing. In this paper, by carefully designing micro-rod templates used for our overgrowth, in particular, the diameter and height of the micro-rods used (two major parameters), we have achieved (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) semi-polar GaN with best crystal quality on sapphire, which has been systematically studied as a function of the micro-rod parameters by means of multiple characterization methods including photoluminescence (PL), transmission electron microscopy (TEM) and X-ray diffraction (XRD).…”

Diffusion-Driven Charge Transport in Light Emitting Devices

“…In III-N technology, SAG has been employed mostly in epitaxial lateral overgrowth (ELOG) methods which were developed to reduce threading dislocations in heteroepitaxial growth [55][56][57]. In contrast with ion implantation, the extensively characterized [58][59][60][61][62] defect-free GaN layers grown by lateral epitaxial over-growth can provide a more beneficial solution to realize LHJ structures [63].…”