Growth of High-Performance M-plane GaN Optical Devices

Brief Description

A method using MOCVD growth conditions to achieve high performance m-plane GaN optical devices, including LEDs and LDs. 

Background

GaN and its alloys (AlGaN, InGaN, AlInGaN) have been established as effective for fabrication of visible and ultraviolet optoelectronic devices and high-power electronic devices. These devices are most often grown along the polar c-direction, using a variety of growth techniques, including molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), or hydride vapor phase epitaxy (HVPE). However, growing devices along the polar c-direction results in charge separation, spontaneous polarization, and degraded device performance. One possible alternative is to grow devices along the m-plane, a nonpolar GaN plane where there is no net polarization, radiative efficiencies should be higher, and no wavelength shift occurs. However, nonpolar GaN devices typically have output powers and efficiencies that are well below c-plane LEDs, mainly due to high dislocation densities. 

Description

Researchers at UC Santa Barbara have invented a method using MOCVD growth conditions to achieve high performance m-plane GaN optical devices, including LEDs and LDs. Key components of the invention include using a low defect density substrate or template, thick quantum wells, a low temperature p-GaN growth technique, and a transparent conducting oxide for the p-contact. It is important that defects and stacking faults are eliminated from the active region, because this decreases the number of non-radiative recombination centers and improves carrier transport properties. The p-type GaN is grown at a much lower temperature than the active region temperature, and transparent conducting oxides are used to enhance light extraction. The method can be extended to the use of a three-color active region, which can produce red, green and blue (RGB) emissions. This results in the emission of white light that is polarized due to the nature of m-plane optical devices. 

Advantages

·         Emission of polarized, white light

·         Very high output powers and high efficiencies

·         Enhanced light extraction due to use of transparent oxide electrode (ITO)

·         Method can be applied to the a-plane or any of the semipolar planes of GaN

Applications

·         LEDs

·         Laser diodes (LDs)

·         Vertical cavity surface emitting lasers (VCSELs)

Patent Status