| In recent years, there has been remarkably rapid progress in the development of high brightness light-emitting diodes (LEDs) based on InGaN/GaN multiple quantum wells (MQWs), which have yielded the commercial high-power blue LEDs with internal quantum efficiency (IQE) as high as 70%. However, as the emission wavelength extends to longer-wavelength region with increasing indium content of the alloy, the efficiency of InGaN based LEDs decrease seriously. The most important reason for that is it is very difficult to obtain high In content (HIC) InGaN with high-crystalline-quality. There are so many crystalline defects in HIC InGaN layers that IQE of LED is drastically decreased. For this reason, the HIC InGaN has attracted considerable attention though several barriers exist in the field.In this dissertation, we fabricated an indium-rich InGaN device structures on fully strain-relaxed InGaN templates by molecular beam epitaxy (MBE). The structural characteristics and chemical composition calculation were applied for the HIC InGaN alloys. Rapid thermal annealing(RTA) were applied in order to improve the crystalline quality alloys and change the mechanism of growth. The main conclusions are listed as follows:(1)In oreder to obtain high-crystalline-quality HIC InGaN alloys, we designed a growing method that fabricated an indium-rich InGaN devices structures on a fully strain-relaxed InGaN template by molecular beam epitaxy in conjunction with a nano-sculpting process using glancing angle ion flux. It is important for the template to be relaxed because its key function is to provide a new lattice parameter for growing indium-rich InGaN alloys. And the nano-sculpting make a greater than 2 orders of magnitude reduction in threading dislocation density in InGaN layers.(2)By XRD and transmission electron microscopy (TEM) characterization techniques, we observed high In content InGaN alloys in a unique kind of micro-structure.The X-ray reflectivity changing with the angle of incidence in the characteristics of the analysis and interpretation of the non-symmetry plane (10-15) in reciprocal space scans explained the reason of MQWs satellite peaks associated with unconventional lateral drift. Meanwhile, according to TEM, we found the InGaN MQWs,grown in the rough interface{10-1m} InGaN film (m> 1), have the showing a strong composition modulation phenomenon in the<10-1m> direction. In that, for the first time, we explained the reason that the InGaN multiple-quantum wells grown on the surface have a strong ability of Induim incorpration. In addtiona, we firstly observed by TEM In/Ga atomic ratio of InGaN and the c-axis direction of the ordered structure of 1:1 in a high spontaneous superlattice structure In InGaN alloy component.(3)By rapid thermal annealing with different experimental conditions, we found that the surface morphology of InGaN p-i-n MQW sample was improved in the condition of nitrogen environment, with 500℃, annealed for 15 minutes. The metal of Indium, attached on surface, was re-incorporated into the p-InGaN layers. Since the V-shaped defects on InGaN surface were shrinked and disappeared, by rapid themal annealing, which made the InGaN Schottky reverse leakage current a reduction of two orders of magnitude.(4)We developed a new method for preparing growing InGaN nano-columns. We found that, in certain condition, the template InGaN would change the surface morphology of the growth of InGaN with situ-annealing, that the subsequent InGaN crystal growth direction (0001) deviation occurs island growth resulting structure can not form a complete closed boundary. So that can spontaneously form the columnar growth mode. Without using traditional metal-induced or complicated methods nano-imprint technology, etc. We can growth InGaN nano-pillar structure in MBE directly. |
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