We report on GaN n-type doping using silane, germane, and isobutylgermane as Si and Ge dopants, respectively. A significant increase in tensile stress during growth is observed for Si doped samples while this is not the case for Ge doping. In addition, Ge can be doped up to 2.9 Â 10 20 cm À3 , while Si doping leads to 3-D growth already at concentrations around 1.9 Â 10 19 cm À3. The free carrier concentration was determined by Hall-effect measurements, crystal quality, and structural properties by x-ray diffraction measurements. Additionally, secondary ion mass spectroscopy and Raman measurements were performed demonstrating the high material quality of Ge doped samples. V
In this paper, we compare the effectiveness of two different methods regarding the reduction of defect densities in heteroepitaxially grown a-plane GaN by heavy Si doping. The insertion of well-established in situ Si x N y nanomasks leads to locally heavy Si d-doped GaN. By increasing the Si x N y deposition time in the range from 0 to 300 s the full width at half maxima (FWHM) of the X-ray diffraction v-scans at inplane GaN(1100) and GaN(0002) Bragg reflections decreases from 0.558 to 0.248 and from 0.458 to 0.168, respectively. When growing without any Si x N y interlayer but instead with continuously heavy Si-doping, these values are further decreased to 0.138 and 0.158, respectively. By measuring several higher order reflections and detailed evaluation of the vscan broadening in Williamson-Hall-plots (WHPs) a considerable reduction in defect densities and no hint of basal plane stacking faults (BSFs) were found for the heavy Si doped aplane GaN sample. To verify this result the micro-structural properties of this sample were additionally investigated by transmission electron microscopy and cathodoluminescence (CL).
The carrier transport in AlGaN light emission diode (LED) structures on Si-substrates including an AlN multilayer (ML) buffer for reduction of defects was investigated using I-Vcharacteristics and admittance spectroscopy. Additionally, AlN on Si ML and AlN/AlGaN:Si on Si structures were grown and analyzed separately. The AlN-ML/AlGaN:Si heterojunction, and the pn-junction including the AlGaN/GaN multi quantum well (MQW)-structure were identified. As the main space charge regions (SCRs) controlling the carrier transport through the ultraviolet-light emission diode (UV-LED) structure the Sisubstrate/AlN-ML heterojunctions pointed out. The I-Vcharacteristic of the LED structure is described by the series resistance of the AlN-ML and a parallel resistance with respect to the pn-junction. Interface defect states and/or deep defects impact the series resistance. The carrier transport through the LED structure is controlled by a tunnel process described by a Fowler-Nordheim (FN)-emission mainly through the AlN-ML buffer forming the series resistance.
Undoped a-plane GaN layers grown by metal organic vapor phase epitaxy on sapphire (10-12) substrates using low temperature GaN seed layers and in-situ SiN masks were characterized by Hall-effect measurements, CV-characteristics and photovoltage spectroscopy. With increasing deposition time of the SiN masks the electron concentrations of the GaN layers are enhanced. The dominant activation energy between 14 meV and 22 meV determined by temperature dependent Hall-effect is very similar to the donor silicon on gallium site. Two other activation energies at 30 meV and between 50 meV and 70 meV were found corresponding well with O Ga and V N defects, respectively. The depth profiles of the net donor densities show a strong increase towards the substrate /LT-GaN/HT-GaN interface indicating diffusion of silicon from the SiN mask towards the surface. Therefore, the Si-doping is attributed to the dissolution of the SiN masks during the following high temperature GaN layer growth. Sidoping from the SiN masks also explains the deterioration of the band bending within the LT-GaN / HT-GaN junction found by photovoltage spectroscopy.
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