Tech Briefs

Chip-scale visible lasers have applications in laser sights, environmental monitoring, full-color displays, and solid-state lighting.

There is a great need to develop chip-scale visible lasers for many applications, including laser sight, environmental monitoring, and compact pumping sources for ultra-short laser pulse generation, high-luminous full-color displays, new-generation solid-state lighting, etc. The realization of chip-scale visible laser diodes (LDs) would provide significant benefits in terms of cost, volume, and the ability of photonic integration with other functional devices. Significant progress in nitride material technology has been achieved, and high-performance visible LEDs and near-UV LDs based on InGaN are now commercially available.

However, many technological challenges remain to be overcome in order to realize InGaN visible injection LDs. The two most outstanding issues are high dislocation density, which causes a premature device breakdown, and low conductivity (or doping efficiency) of p-type GaN, which limits an efficient current injection. The objective of this research is to develop improved growth and doping methods for achieving GaN and A1InGaN alloys with improved crystalline quality and conductivity, and to aid in the development of III-nitride visible injection LDs operating at around 500 nm.

The attainment of single-phase InGaN alloys inside the previously thought miscibility gap by MOCVD may be attributed to the following factors: the presence of biaxial strain between the InGaN thin film and the GaN or A1N epitemplate; non-equilibrium growth processes taking place in epitaxial growth techniques like MOCVD; and relatively low growth temperatures (the growth temperature varied from 730 to 610 °C as the In-content was increased from 25% to 63%).

MOCVD processes were successfully transferred for producing high-quality AlN epilayer templates, which were developed in a growth system, to production scale systems with six pieces of 2" wafer capability. This a critical step, as this capability enables an ample supply of templates to make multiple runs per day, which is necessary for the development of growth processes for green LD structures. Furthermore, the crystalline quality of these AlN epitemplates was improved, as evidenced by a decrease in the FWHM of the XRD rocking curve of the asymmetric reflection peak from greater than 400 arcsec to below 300 arcsec.

The green light emitting diode (LED) structure was increased to 500-nm LD structure by inserting cladding and light guiding layers. A significant improvement in optical emission efficiency was

obtained by depositing the emitter structures on AlN templates.

This work was done by Jingyu Lin and Hongxing Jiang of Kansas State University for the Army Research Office. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Photonics category. ARL-0110

This Brief includes a Technical Support Package (TSP).

AlInGaN Bandgap and Doping Engineering for Visible Laser Diodes (reference ARL-0110) is currently available for download from the TSP library.

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