Epitaxial growth of GaN films on unconventional oxide substrates

Abstract

The unconventional oxide substrates have been used for the growth of high-quality GaN films due to their relatively small lattice and thermal expansion coefficient mismatches with GaN. This review focuses on the recent progress and discusses the perspectives of the epitaxial growth of GaN films on unconventional oxide substrates.

Epitaxial growth of group III-nitride films by pulsed laser deposition and their use in the development of LED devices

“…Meanwhile, sapphire has a low thermal conductivity of $ 25 W/m K that hinders the thermal dispatch during the device application and hence the development of high-power group III-nitride devices. What's more, group III-nitride devices prepared on sapphire are mainly along the [0001] c-axis, where strong spontaneous and strained-induced piezoelectric polarization exist [7][8][9][10]. The internal electric field caused by this polarization leads to the separation of carriers in the quantum wells (so called quantum-confined Stark effect, QCSE) and thereby a reduced quantum efficiency and a quicker efficiency droop [7][8][9][10].…”

“…At present, sapphire is still the most popular commercial substrate for epitaxial growth of group III-nitride devices. However, due to the relatively large lattice mismatch between sapphire and group III-nitrides, high-density dislocations still exist in the group III-nitride devices, which may serve as nonradiative recombination centers, and eventually deteriorate the performance of group III-nitride devices [8][9][10]. Meanwhile, sapphire has a low thermal conductivity of $ 25 W/m K that hinders the thermal dispatch during the device application and hence the development of high-power group III-nitride devices.…”

“…The internal electric field caused by this polarization leads to the separation of carriers in the quantum wells (so called quantum-confined Stark effect, QCSE) and thereby a reduced quantum efficiency and a quicker efficiency droop [7][8][9][10]. One of the most effective approaches to build group III-nitride devices is based on nonpolar planes including (11 À 20) a-and (1 À 100) m-planes [7][8][9][10], because the QCSE is eliminated in the nonpolar group III-nitride devices and accordingly the efficiency is improved. In addition, the price for sapphire is still quite expensive, which raises the cost for the commercialization of group III-nitride devices.…”

“…What's more, group III-nitride devices prepared on sapphire are mainly along the [0001] c-axis, where strong spontaneous and strained-induced piezoelectric polarization exist [7][8][9][10]. The internal electric field caused by this polarization leads to the separation of carriers in the quantum wells (so called quantum-confined Stark effect, QCSE) and thereby a reduced quantum efficiency and a quicker efficiency droop [7][8][9][10]. One of the most effective approaches to build group III-nitride devices is based on nonpolar planes including (11 À 20) a-and (1 À 100) m-planes [7][8][9][10], because the QCSE is eliminated in the nonpolar group III-nitride devices and accordingly the efficiency is improved.…”

“…Recently, group III-nitrides such as AlN [1,2], GaN [3][4][5], and InN [6], as well as their alloys have attracted remarkable considerations due to their inherent properties [7][8][9], which make them possible for applications in optoelectronic devices [10]. At present, sapphire is still the most popular commercial substrate for epitaxial growth of group III-nitride devices.…”