Uv-Blue Lasers Based on Ingan/Gan/Al₂O₃ and on Ingan/Gan/Si Heterostructures

Abstract

InAlGaN compounds are very promising for light emitting devices such as light emitting diodes (LED) and laser diodes (LD) due to their wide interval of the band gap energy (ultraviolet — orange spectral region), chemical, thermal and mechanical stability [1]. The GaN-based material system has gained much attention also for electronic applications due to its outstanding inherent electrical properties such as high breakdown voltages, high peak electron velocities and high sheet electron concentration especially in two- dimensional electron gas structures. A current focus of the device research are high electron mobility transistor (HEMT) devices [5] and ultraviolet detectors 6] grown on sapphire and silicon carbide. The AlInGaN based LEDs have an output power of about 14 mW with power density of about 300 kW/cm² at low operating voltage and current of 3 V and 20 mA [1], AlGaInP LEDs can operate in the red region of the visible spectrum up to 620 nm with luminous intensity up to 40 lumens [1]. The GaN based LEDs grown on sapphire substrates become as bright and efficient as incandescent bulbs over the ultraviolet and visible wavelengths. If the LED efficiency would be achieved up to 50% and more, for example a 200 lm/W, white light sources two times more efficient than fluorescent lamps and ten times more efficient than incandescent lamps can be produced. The world energy saving would be more than 1,000 TWh/year. An important place among these devices belongs to lasers. The violet lasers have lifetime up to 15000 hours with power of 30 mW [4].