Oxford Instruments produces semi-polar GaN layers

The technical team at Oxford Instruments-TDI, led by Dr Alexander Usikov, is working closely with a light-emitting diode (LED) manufacturer to make semi-polar GaN layers for optoelectronic devices.

This would increase radiative recombination efficiency and device performance.

In the past decade, Group III-nitride materials have been widely used for visible and ultraviolet LEDs and blue, violet laser diodes.

Most of these optoelectronic devices are typically fabricated on conventional polar (0001) c-plane oriented substrate materials.

Devices grown on the polar substrate orientation suffer undesirable spontaneous and piezoelectric polarisation, resulting in significant band bending in the quantum well, which reduces radiative recombination efficiency and lowers device performance.

In order to diminish these polarisation effects, growth of GaN-related devices along semi- and non-polar directions has been studied intensely.

Using hydride vapour phase epitaxy (HVPE), the team has grown high-quality, semi-polar (11.2) oriented GaN on (10.0) m-plane sapphire with an intermediate layer between the sapphire substrate and the GaN layer.

The semi-polar (11.2) GaN layers were grown in a temperature range from 930C to 1,050C in an inert argon ambient at atmospheric pressure.

Gallium and aluminium were used as metallic source materials and hydrogen chloride (HCl) and ammonia (NH3) as the active gases for the HVPE process.

The epitaxial growth of GaN was performed at approximately 60m/hour using an intermediate layer deposited on m-plane sapphire followed by an undoped GaN layer.

The growth procedure is said to result in a high-quality, semi-polar GaN layer with a thickness up to 30 mm.

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