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HL: Fachverband Halbleiterphysik

HL 34: Nitrides: Dots, rods, and structures

HL 34.4: Talk

Tuesday, March 17, 2015, 12:00–12:15, EW 201

Highly reflective distributed Bragg reflectors for LEDs by modulation doped GaN:Ge — •Christoph Berger, Armin Dadgar, Jürgen Bläsing, Peter Veit, and André Strittmatter — Otto-von-Guericke-Universität Magdeburg

We report on the growth of strain-free, vertically conductive nitride-based Bragg reflectors for LED applications by taking advantage of the Burstein-Moss-effect in highly Ge-doped GaN. The Burstein-Moss-effect describes an increase of the effective bandgap for high carrier concentrations leading to a reduction of the refractive index of the layer. Significant changes of the refractive index can be achieved for carrier concentrations of the order of 1020 cm-3 which is possible in GaN using Ge-doping. For such doping levels, the refractive index of GaN:Ge is reduced to GaN:uid by more than 2 % at a wavelength of 430 nm . We have grown reflectors with 60 periods of GaN:Ge/GaN:uid. Layer growth was monitored by in-situ metrology and no degradation of the layer structure was observed. Close to the targeted wavelength at 430 nm, a stopband centered at 426 nm wavelength with a maximum reflectivity of 60 % was found, which is below the expected reflectivity of 90 %. The reasons for this are under investigation. An InGaN/GaN multiple quantum well grown on top of a 100-pair GaN:Ge/GaN:uid DBR shows significantly altered photoluminescence spectra compared to MQWs grown on an undoped GaN buffer. The spectra of MQW grown on the GaN:Ge/GaN:uid DBR exhibits a drastically reduced linewidth and doubled emission intensity.