Characteristics of the surface microstructures in thick InGaN layers on GaN (original) (raw)
Related papers
Structural and optical properties of InGaN/GaN layers close to the critical layer thickness
Applied Physics Letters, 2002
Structural and optical properties of InGaN / GaN multiple quantum wells ͑MQWs͒ grown on nano-air-bridged GaN template by metal organic chemical vapor deposition were investigated. The InGaN / GaN MQWs on nano-air-bridged GaN demonstrate much better surface morphology, revealing low defect density ϳ4 ϫ 10 8 cm −2 with step flow features measured by atomic force microscopy. The photoluminescence measurement shows one magnitude higher in intensity from less defective InGaN MQWs compared to that of the control InGaN MQWs. The improvement in photoluminescence of the InGaN MQWs is benefited from the reduction of threading dislocation density in the InGaN / GaN active layers and GaN template, revealed from cross-sectional transmission electron microscopy. High resolution x-ray diffraction analysis results show higher indium mole fraction in the MQWs when grown on nano-air-bridged GaN template, due to the strain relaxation in the nano-air-bridged GaN template. This higher indium incorporation is consistent with the redshift of the photoluminescence peak.
Microstructural characterization of InGaN/GaN multiple quantum wells with high indium composition
Journal of Crystal Growth, 2001
The microstructural study of InGaN/GaN multiple quantum well (MQW) structures with high In (indium) composition (>30%) has been performed using transmission electron microscopy (TEM). The increased strain in InGaN/GaN MQWs by high In composition is relaxed by the formation of several defects such as dislocations, stacking faults, V-defects, and tetragonal shape defects. High-resolution TEM (HRTEM) measurement shows a new formation mechanism of V-defects, which is related to the stacking mismatch boundary induced by stacking faults. These Vdefects result in different growth rates of the GaN barriers according to the degree of the bending of InGaN well layers, which changes the period thickness of the superlattice. In addition, evidence of In clustering is directly observed both by using an In ratio map of the MQWs and from In composition measurements along an InGaN well using energy filtered TEM (EFTEM). r
Investigation of structural, optical and morphological properties of InGaN/GaN structure
Applied Physics A, 2018
In this study, InGaN/GaN structure is investigated in the temperature range of 300-500 °C with steps of 50 °C. InGaN/ GaN multi-quantum well structure is deposited on c-orientated sapphire wafer by metal organic chemical vapour deposition method. All the parameters except for temperature kept constant during growth period. InGaN/GaN structures with different In content are investigated by XRD technique. Their structural, optical and morphological characteristics are determined by high resolution X-ray diffraction, Fourier transform spectroscopy (FTIR), photo luminescence (PL), transmission and atomic force microscopy (AFM). According to FTIR and PL spectra's, it is noticed that band gap values coincide with blue region in the electromagnetic spectrum. As a result of transmission measurements it is seen that light is completely absorbed by the sample at approximately 390 nm. Using XRD technique, dislocation densities and strain are calculated. Full width at half maximum of the XRD peak values gained from X-ray diffraction are used in an alternative method called Williamson-Hall (W-H). Using W-H method, lateral and vertical crystal lengths and tilt angles are determined. Surface roughness parameters are investigated by AFM. Different properties of GaN and InGaN layers are compared as dependent on increasing temperature. According to AFM images it is seen that these structures have high surface roughness and large crystal size. All the results yielded from the mentioned methods are in good agreement with the previous works done by different authors.
Journal of Alloys and Compounds, 2019
InGaN/GaN heterostructures were grown on c-plane sapphire substrates using metal organic chemical vapour deposition by varying the trimethylindium flow rate as 7, 10 and 14 µmole/min. The structural, morphological, optical and electrical properties of InGaN layers were investigated. Crystalline quality, dislocation densities comprising of screw and edge types in InGaN and GaN layer have been analyzed using High-Resolution X-ray Diffractometer (HRXRD). The composition of Indium (In) in the InGaN layers was estimated around 8-10% which was found to be dependent on the In flow rate. The strain between InGaN and underlying GaN layer have been analyzed through reciprocal space mapping studies along the (1 0-1 5) plane in InGaN/GaN heterostructures. The features of V and trench defects were observed using scanning electron microscopy and atomic force microscopy respectively. The V and trench defect density has been correlated with the pre-existing threading dislocation density estimated using HRXRD measurements. Also the trench defects were observed to be a coalescence of V defects in InGaN layers. The photoluminescence results showed that band edge emission peaks of three different points (primary flat, centre, and Edge) were observed. These peak variations were found to be red shift behavior in all three points. These variations were due to the fluctuations in the Indium composition and corresponding trench & V defects respectively. The Hall measurements exhibit an alteration in semiconducting behavior with respect to V and trench defect surrounded InGaN layers. And also realized that compressive strain in underlying GaN can lead the high sheet concentration compared to the tensile strained underlying GaN layer. It clearly suggests that the V and trench defect surrounded InGaN layers contain the suitable candidates for next generation optoelectronics applications.
V-defects and dislocations in InGaN/GaN heterostructures
Thin Solid Films, 2005
In the growth of InGaN/GaN multi-quantum well (MQW) heterostructures by metal organic chemical vapor deposition, V-defects attached to threading dislocations have been observed and investigated. Energy-dispersive X-ray analysis and conventional transmission electron microscopy studies were carried out in order to determine the In composition and investigate the behavior of the dislocations. The Vdefects are limited by {1011} lattice planes, they are attached to threading dislocations and may start at the third quantum well. The associated dislocation runs up into the overgrown GaN layer. Some (a+c) dislocations were shown to decompose inside the multi-quantum well, giving rise to a misfit segment in the c-plane and a V-shape defect. D
2008 33rd IEEE Photovolatic Specialists Conference, 2008
The III-nitride material system with band gap ranging from 0.7eV to 6.2eV has substantial potential to develop high-efficiency solar cells. The III-nitride materials are grown by MOCVD on a lattice mismatched sapphire substrate (0001). This paper presents the generation of extended crystalline defects and their spatial distribution in the GaN and In0.12Ga0.88N layers as a function of In0.12Ga0.88N thickness. The material is characterized by photoluminescence, and the primary peak intensity is observed to increase with thickness, up to 200 nm, but the intensity diminishes with further increase in thickness. Additional photoluminescence peaks are observed for In0.12Ga0.88N thicknesses greater than 100 nm. These observations are attributed to extended crystalline defects and are characterized by high resolution x-ray diffraction. A detailed analysis of these extended crystalline defects is presented based on rocking curves, symmetric and asymmetric reciprocal space maps. The crystalline defects are unavoidable during epitaxial growth, but knowledge of their generation process yields better control over them.
Observation of V Defects in Multiple InGaN/GaN Quantum Well Layers
MATERIALS TRANSACTIONS, 2007
Multiple In 0:18 Ga 0:82 N (4 nm)/GaN (40 nm) quantum well (QW) layers in a green laser diode were observed by high-angle annular darkfield (HAADF) scanning transmission electron microscopy (STEM) and conventional transmission electron microscopy. HAADF-STEM provided undoubted evidence that V defects in the multiple QW have the thin six-walled structure with InGaN/GaN {10 1 11} layers. The detailed structure of the observed V defects is discussed on the basis of the formation mechanism of V defects which was proposed taking into account the growth kinetics of the GaN crystal and a masking effect of In atoms segregated around the threading dislocation (Shiojiri et al.
Growth and properties of InGaN nanoscale islands on GaN
Journal of Crystal Growth, 1998
Strong photoluminescence and radiative recombination lifetimes longer than 1 ns at room temperature have been observed in GaN/Si/InGaN/GaN structures containing InGaN submicron islands. The flat islands, with a width at their base in the order of 200 nm and a height in the order of 1-2 nm, grow in a spiral mode around dislocations with partial or pure screw character after a passivation of the GaN surface by a preflow of disilane. Their surface density is comparable to the dislocation density of the GaN layer in the order of 10-10 cm\.