News

10 March 2009

 

HVPE of semi-polar GaN on m-plane sapphire boosts opto device performance

The technical team at Oxford Instruments-TDI, led by Dr Alexander Usikov, says that it has made significant progress in fabricating semi-polar gallium nitride layers for optoelectronic devices (which should increase radiative recombination efficiency and device performance), and is working closely with a leading LED manufacturer.

 

Graph: demonstrates the XRD w-scan rocking curve of symmetric (11.2) reflex measured for a 2-inch (11.2) GaN/m-plane sapphire wafer.

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. However, devices grown on a polar substrate orientation suffer undesirable spontaneous and piezoelectric polarization, resulting in significant bending of the energy bands in the quantum well layers of the structure. This reduces radiative recombination efficiency, limiting the light-emission performance.

Picture: the optical micrograph (image width of 60μm) of (11.2) oriented GaN layer grown on m-plane sapphire. Atomic force microscope (AFM) results show the rms surface roughness of 3.7nm for a 2μm x2μm scan.

To diminish these polarization effects, the growth of GaN-related devices along semi-polar and non-polar directions has been studied intensively. Using hydride vapour phase epitaxy (HVPE), the Oxford Instruments-TDI 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 the temperature range 930-1050ºC in an inert argon ambient at atmospheric pressure. Gallium and aluminum 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 a rate of about 60μm/ hour using an intermediate layer deposited on m-plane sapphire followed by an undoped GaN layer.

The firm says that this growth procedure results in a high-quality, semi-polar GaN layer with a thickness of up to 30μm.

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See: Oxford Instruments Company Profile

Search: Oxford Instruments TDI LEDs Blue-violet laser diodes HVPE GaN Sapphire

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