Interaction between dislocations density and carrier concentration of gallium nitride layers (original) (raw)
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Influence of dislocation density on photoluminescence intensity of GaN
Journal of Crystal Growth, 2005
The influence of dislocation density on photoluminescence intensity is investigated experimentally and compared to a model. GaN samples were grown by molecular beam epitaxy and metal-organic chemical vapour deposition. Different growth parameters and thicknesses of the layers resulted in different dislocation densities. The threading dislocation density, measured by atomic force microscopy, scanning electron microscopy and X-ray diffraction, covered a range from 5 Â 10 8 to 3 Â 10 10 cm À2. Carrier concentration was measured by capacitance-voltage-, and Hall effect measurements and photoluminescence at 2 K was recorded. A model which accounts for the photoluminescence intensity as a function of dislocation density and carrier concentration in GaN is developed. The model shows good agreement with experimental results for typical GaN dislocation densities, 5 Â 10 8-1 Â 10 10 cm À2 , and carrier concentrations 4 Â 10 16-1 Â 10 18 cm À3 .
Dislocation effect on light emission efficiency in gallium nitride
Applied Physics Letters, 2002
We modify the model of non-radiative carrier recombination on threading dislocation cores [Z. Z. Bandić, P. M. Bridger, E. C. Piquette, and T. C. McGill, Solid-State Electronics 44, 221 (2000)] to estimate quantitatively the light emission efficiency in GaN as a function of the dislocation density and non-equilibrium carrier concentration. The model predictions are in good agreement with available data on the minority carrier diffusion length in GaN. The dislocation density must be reduced, at least, down to ~10 7 cm -2 in order to provide a light emission efficiency close to unity. The n-type background doping is found to be favorable for the further efficiency improvement.
Journal of Electronic Materials, 2020
Electrical and optical properties of grown-in and freshly introduced dislocations in GaN have been studied by the electron beam induced current and cathodoluminescence methods. It is observed that the recombination properties of grown-in and freshly introduced basal plane and threading dislocations are comparable. That allows to assume the intrinsic nature of dislocation recombination activity in GaN. It is demonstrated that the recombination properties of basal plane dislocations weakly depend on their type. The behavior of dislocation-related luminescence at 3.1 eV is more complex. It can be observed not in all GaN crystals even when dislocations are introduced in the similar conditions. Besides, it is not observed on basal plane and threading grown-in dislocations. This luminescence is not produced by freshly introduced basal plane dislocations. These observations can be explained assuming that the dislocation-related luminescence is associated with point defects generated by dislocations gliding in pyramidal or prismatic slip planes.
Studies on the dislocation densities of gallium nitride grown by MOCVD
16th International Workshop on Physics of Semiconductor Devices, 2012
Group III-V nitrides have become versatile semiconducting materials for short wavelength LEDs, high temperature transistors. The growth and device processing of these materials are significant due to unusually high bond energies of nitrides. Inspite of high dislocations densities in the order of 10 9 cm-2 the optical and electronic devices based on nitrides show high performance compared to conventional semiconductor devices. Understanding of the behavior of dislocations in these materials structures are very important for the fabrication of devices. In the present study, GaN was grown on sapphire substrates using MOCVD. The dislocation density of GaN has been estimated by wet etching and HRXRD. The results have been correlated with the growth conditions. The dislocation density of the samples was found to be between 3.5x10 9 cm-2 and 5.0x10 8 cm-2 .
Charge accumulation at a threading edge dislocation in gallium nitride
Applied Physics Letters, 1999
We have performed Monte Carlo calculations t.o determine the charge accumulation on &reading edge dislocations in GaN as a function of the dislocation density and background dopant density. Four possible core structures have been examined, each of which produces defect levels in the gap and may therefore act as electron or hole traps. Our results indicate that charge accumulation, and the resulting electrostatic interactions, can change the relative stabilities of the different. core structures. Structures having Ga and N vacancies at the dislocation core are predicted to be st.able under nitrogen-rich and gallium-rich growth conditions, respectively. Due to dopant depletion at. high dislocat.ion density and the rnult.itude of charge states, the line charge exhibits complex crossover behaxior as the dopant. and dislocat.ion densities vary. Gallium nit,ride films grown on sapphire substrates t y p ically contain bet.ween lo8 and 1O'O threading dislocations per cm2 as a result* of the subst,ant,ial film-substrate chemical and 1att.ice mismatch.l Nevertheless, it. has been possible t.0 fabricate bright and efficient light,-emitt.ing diodes from films composed of GaN alloyed wit.h InN and A1N.2 This success led several researchers t.o specu1at.e early on t.hat t.hreading dislocat.ions in GaN might not act. as efficient. minority-carrier recombination sit.es.' Recent. experiment.al studies, however, have confirmed that there is significant opt.ica13 and elect.rica14 activity associat,ed with these defects. In particular, results from a recent. scanning-capacit.ance microscopy study5 suggest that dislocations are negatively charged in n-type GaN, and studies of transverse mobility in n-type GaN indicate that elect,rons are scattered from these negatively charged dislocations.
Reduction of dislocation density in heteroepitaxial GaN: role of SiH4 treatment
Journal of Crystal Growth, 2004
TEM and AFM data show that a significant reduction of threading dislocations in heteroepitaxial GaN/Al 2 O 3 grown by MOCVD has been achieved. The reduction has been obtained by growth interruption followed by annealing in silane (SiH 4 ). Density of threading dislocations in the GaN layer above the silane-exposed surface decreased to 5 Â 10 7 cm À2 in comparison to 10 9 cm À2 in the layer below this surface. TEM data showed the existence of pyramidal pits at the silane-exposed surface. They were overgrown by the subsequent GaN layer. The presence of these pits indicates that the GaN surface was selectively etched during the silane flow. These pits were sites where dislocations drastically changed propagation direction from parallel to the c-axis to horizontal. Horizontal propagation of dislocations above the surface treated by silane (where formation of SiN was expected) suggests that the GaN layer in this region was grown in the lateral epitaxial overgrowth mode. EDX measurements performed at the interface between the SiH 4 -treated GaN layer and the subsequently grown GaN did not show any presence of Si. Therefore, it is believed that the dislocation reduction is related to the lateral overgrowth above the pits and not to the formation of a SiN interlayer. r
Journal of Applied Physics, 2003
Cathodoluminescence technique combined with transmission electron microscopy (TEM-CL) has been used to characterize optical properties of dislocations in GaN epilayers. The dislocations act as nonradiative centers with different recombination rates. TEM-CL observation showed that even for the same Burgers vector of a, the dislocations show different electrical activity depending on the direction of dislocation line, i.e., the edge-type dislocation parallel to the c plane is very active, while the screw-type one is less active. The simulation of the CL images gives us the information of parameters such as carrier lifetime and diffusion length. (C) Cathodoluminescence technique combined with transmission electron microscopy ͑TEM-CL͒ has been used to characterize optical properties of dislocations in GaN epilayers. The dislocations act as nonradiative centers with different recombination rates. TEM-CL observation showed that even for the same Burgers vector of a, the dislocations show different electrical activity depending on the direction of dislocation line, i.e., the edge-type dislocation parallel to the c plane is very active, while the screw-type one is less active. The simulation of the CL images gives us the information of parameters such as carrier lifetime and diffusion length.
Influence of dopants and substrate material on the formation of Ga vacancies in epitaxial GaN layers
Physical Review B, 2001
We have applied a low-energy positron beam and secondary ion mass spectrometry to study defects in homoepitaxial and heteroepitaxial GaN layers. Positron experiments reveal high concentrations of Ga vacancies in nominally undoped n-type GaN, where the conductivity is due to unintentional oxygen incorporation. Ga vacancies are observed in both homoepitaxial and heteroepitaxial layers, indicating that their formation is independent of the dislocation density. No Ga vacancies are detected in p-type or semi-insulating samples doped with Mg, as predicted by the theoretical formation energies. In samples where n-type conductivity is due to Si doping and the incorporation of oxygen impurities is suppressed, the concentration of Ga vacancies is much lower than in n-type samples containing oxygen. This indicates that the presence of oxygen donor in GaN promotes the formation of Ga vacancy. We suggest that this effect is due to the creation of V Ga-O N complexes during the epitaxial growth.
Coincident Electron Channeling and Cathodoluminescence Studies of Threading Dislocations in GaN
Microscopy and Microanalysis, 2014
We combine two scanning electron microscopy techniques to investigate the influence of dislocations on the light emission from nitride semiconductors. Combining electron channeling contrast imaging and cathodoluminescence imaging enables both the structural and luminescence properties of a sample to be investigated without structural damage to the sample. The electron channeling contrast image is very sensitive to distortions of the crystal lattice, resulting in individual threading dislocations appearing as spots with black-white contrast. Dislocations giving rise to nonradiative recombination are observed as black spots in the cathodoluminescence image. Comparison of the images from exactly the same micron-scale region of a sample demonstrates a one-to-one correlation between the presence of single threading dislocations and resolved dark spots in the cathodoluminescence image. In addition, we have also obtained an atomic force microscopy image from the same region of the sample, which confirms that both pure edge dislocations and those with a screw component~i.e., screw and mixed dislocations! act as nonradiative recombination centers for the Si-doped c-plane GaN thin film investigated.