SummaryThin films incorporating GaN, InGaN and AlGaN are presently arousing considerable excitement because of their suitability for UV and visible light-emitting diodes and laser diodes. However, because of the lattice mismatch between presently used substrates and epitaxial nitride thin films, the films are of variable quality.In this paper we describe our preliminary studies of nitride thin films using electron backscattered diffraction (EBSD). We show that the EBSD technique may be used to reveal the relative orientation of an epitaxial thin film with respect to its substrate (a 90 ° rotation between a GaN epitaxial thin film and its sapphire substrate is observed) and to determine its tilt (a GaN thin film was found to be tilted by 13 ± 1 ° towards [10 0] GaN ), where the tilt is due to the inclination of the sapphire substrate (cut off-axis by 10 ° from (0001) sapphire towards (10 0) sapphire ). We compare EBSD patterns obtained from As-doped GaN films grown by plasma-assisted molecular beam epitaxy (PA-MBE) with low and high As 4 flux, respectively. Higher As 4 flux results in sharper, better defined patterns, this observation is consistent with the improved surface morphology observed in AFM studies. Finally, we show that more detail can be discerned in EBSD patterns from GaN thin films when samples are cooled.

No abstract

We have investigated the properties of a commercial light-emitting diode (LED) structure containing an InGaN single quantum well (SQW) by scanning tunneling luminescence (STL). Data was acquired under ambient conditions, i.e., in air and at room temperature, using our unique STL microscope with a novel light collection geometry. Scanning tunneling microscopy (STM) images revealed the presence of hexagonal pits in the structure, with STL images showing strong luminescence from these pits. The variation of STL intensity with bias voltage shows the STL threshold at --2.1 V is numerically similar to the peak position of the SQW luminescence band. A slight shoulder at --2.8 V corresponds to the plateau of the delocalised absorption profile, observed in macroscopic measurements. The peak observed at --3.2 V is close to the observed GaN band edge emission.

In this paper we report room temperature CL studies of a 5 period InGaN (3 nm)/GaN (7 nm) multiple quantum well (MQW) with a nominal indium concentration of 15%, grown on and off a 4.8 mm epitaxially lateral overgrown GaN (ELOG) epilayer. The ELOG epilayer was overgrown through a SiO 2 striped mask with 3 mm window and SiO 2 stripe widths oriented in the GaN h1 " 100i direction by metalorganic vapour phase epitaxy (MOVPE). We show that the luminescence efficiency of both the GaN and the MQW is improved for material lying above the stripes of the SiO 2 mask compared to that above the windows of the mask or unpatterned material. Monochromatic CL images were acquired from both the GaN and MQW layers with the emission from the MQW layer being much brighter than that from the GaN. Marked differences are observed between corresponding CL images acquired at different electron beam energies.

In this paper we illustrate the application of electron beam techniques to the measurement of strain, defect and alloy concentrations in nitride thin films. We present brief comparative studies of CL spectra of AlGaN and InGaN epilayers and EBSD patterns obtained from two silicon-doped 3 μm thick GaN epilayers grown on an on-axis (0001) sapphire substrate and a sapphire substrate misoriented by 10° toward the m-plane (10 0).