Study On Fabrication Of GaN-based Light-emitting Diodes

Gallium nitride (GaN) is a wide band gap semiconductor material with a hexagonal wurtzite crystal structure. At room temperature, its direct band gap is 3.39eV.It's the representation of the third generation semiconductor, with the following advantages: high thermal conductivity, insoluble in acids and base, hardness etc. GaN material is extensively fabricated Laser diode, Light-emitting diode (including green, blue, UV) and high-temperature power devices for its unique property. Light-emitting diode is the semiconductor device, which directly turn electrical energy into light. As compared with conventional light source, light-emitting diode has the properties: long life, low energy-consumed, high reliability etc.In this paper, epitaxy growth of GaN, fabrication of GaN-based LED chip are studied .The main results are as follows:1) InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with Indium tin oxide (ITO) and Ni/Au p-contacts have been successfully fabricated. ITO (500 nm) and Ni/Au (2nm/9nm) films were deposited onto p-GaN epitaxial layers by e-beam evaporation system. For the LEDs with in situ annealed ITO and Ni/Au contacts, the 20 mA forward voltage was 3. 5 V and 3.2 V, respectively. Moreover, under the same amount of injection current, the LED with in situ annealed ITO p-contact had higher output electroluminescence (EL) intensity and larger light output power. The ITO processing enhanced the light output power by 60% compared to the Ni/Au processing. The light output and power conversion efficiency of ITO LEDs on GaN were greatly improved at high injection currents. The fabricated LEDs were subjected to a stress test at 30 mA and 55℃ and showed very small degradation of optical power (<1% decrease) for 24 hrs stress. The light output of MQW LEDs keeps 80% of the original value after 1000 hrs stressing. The fabricated LED devices have demonstrated a good reliability.2) To improve the extraction efficiency of GaN-based light-emitting diodes (LEDs), surface-textured Indium-Tin-Oxide (ITO) transparent ohmic contact layers have been fabricated by utilizing inductively coupled plasma etching technology and natural lithography with3) polystyrene spheres as the etching mask without destroying the P-GaN. The morphologies of the textured ITO surface were examined and characterized by a scanning electron microscope. The optimized and detailed parameters of the texturing process are reported. The fabricated LEDs with the surface-textured ITO ohmic contacts produce a luminance intensity that exceeds that of the traditional planar-surface LEDs by around 70% at 20 mA dc current.4) GaN epitaxy layer with a naturally textured surface was deposited on sapphire substrate by a growth-interruption. Experimental results indicated that GaN-based LED with textured surface exhibit an enhancement in light output power of 60%. The typical 20 mA-driven forward voltage is only 0. 15 V higher than that of conventional LEDs.