This dissertation focuses on understanding the mechanism of threading dislocation reduction in GaN by “in-situ” SiH4 treatment. The effects of SiH4 treatment temperature and time are investigated. By optimizing the SiH4 treatment conditions, two-order dislocation density reduction is obtained, from 9.2 × 109 cm-2 (control sample) to 6.3 × 107 cm-2 in the sample with 20-minute SiH4 treatment at 1100 °C.

The low dislocation density (6.3 × 107 cm-2) GaN material has superior properties as compared to the control sample (dislocation density 9.2 × 109 cm-2). High-resolution x-ray-diffraction (HR-XRD) rocking curves show that full width at half maximum (FWHM) decreases from 0.09 ° to 0.07 ° for (0002) symmetric measurements; and for the (10-12) asymmetric measurements, FWHM decreases from 0.29 ° to 0.07 °. Room temperature photoluminescence (RT-PL) intensity increases 50 times. Carrier lifetime increases from 89 ps to 3.63 ns.

A novel SiH4-assisted, three-dimensional (3D) nucleation model is established to explain the mechanism for threading dislocation reduction in GaN by “in-situ” SiH4 treatment. The treatment changes the growth mode from two-dimensional (2D) to three-dimensional (3D) by revealing threading dislocations. The exposed dislocations serve as the nucleation sites. After SiH4 treatment, the following lateral growth bends the propagating direction of threading dislocations to the basal plane, therefore reducing the dislocation density in the top GaN layer.

The application of these low dislocation density GaN films in 410 nm light emitting diodes (LEDs) is demonstrated. The defect reduction increases the output power by a factor of 2.5.