Method for Increasing GaN Substrate Area in Nitride Devices

Brief Description

A technique for producing large-area, high-quality freestanding non-polar and semi-polar nitride substrates via multiple slicing and growth steps. 

Background

Gallium nitride (GaN) and its compounds that incorporate aluminum and indium have been well established for fabrication of optoelectronic devices and high-power electronic devices. Typically, these devices are grown epitaxially using growth techniques such as molecular beam epitaxy, metalorganic chemical vapor deposition, and hydride vapor phase epitaxy. These methods in current nitride technology employ nitride films that are grown along the polar c-direction, where multiple basal plane axes of GaN and its alloys are aligned perpendicular to the c-axis. However, these devices suffer from the quantum-confined Stark effect (QCSE), which causes spontaneous polarizations.

One possibility for eliminating spontaneous polarization in GaN optoelectronic devices is to grow them on non-polar planes of the crystal. Subsequent non-polar layers are equivalent to the top plane, assuring the bulk crystal will not be polarized along the growth direction. 

Description

Researchers at the University of California, Santa Barbara have developed a technique for producing large-area, high-quality freestanding non-polar and semi-polar nitride substrates via multiple slicing and growth steps. The available surface area is increased geometrically by changing the growth direction of thick-film growth steps. Multiple growth steps with different growth directions that are not orthogonal to the prior substrate surface are utilized, which enlarges the surface area of the final crystal plane. The number of process repeats (growth/slice/polish) and the angles of the slice steps depend on the final crystal plane. This invention is pertinent to all nitrides, and results in reduced defect densities.  

Advantages

·         Total polarization is eliminated (non-polar) or reduced greatly (semi-polar)

·         Improved device performance

·         Applicable to all nitride-based optoelectronic devices

Applications

·         Optoelectronic devices (LEDs, LDs)

·         High-power electronic devices (transistors)

Patent Status