The m-plane InN (1100) epilayers have been grown on a LiAlO2 (100) substrate by a two-step growth method using a metal-organic chemical vapor deposition (MOCVD) system. The low temperature InN buffer layer (LT-InN) is introduced to overcome the drawbacks of thermal instability of LiAlO2 (LAO) and to relieve the strains due to a large thermal mismatch between LAO and InN. Then the high temperature m-plane InN (1100) epilayers (HT-InN) were grown. The results of X-ray diffraction (XRD) suggest that the m-plane InN (1100) epilayer is a single crystal. The X-ray rocking curves (scans) (XRC) and atomic force microscopy (AFM) indicate that the m-plane InN (1100) epilayer has anisotropic crystallographic properties. The PL studies of the materials reveal a remarkable energy band gap structure around 0.70 eV at 15 K.
The in-plane optical anisotropic properties of the non-polar a-plane GaN films grown by metal organic chemical vapour deposition are investigated by using polarised photoluminescence(PL),optical transmission and Raman scattering measurements.Through polarised PL and transmission spectra,the in-plane optical anisotropic properties of a-plane GaN film are found,which are attributed to the topmost valance band(atΓpoint)split into three sub-bands under anisotropic strain.The PL spectra also exhibit that the light hole band moves up more rapidly than the spin-orbit crystal-field spilt-off hole band with the increasing in-plane anisotropic compressive strain.Raman scattering spectra under different configurations further indicate the in-plane anisotropy and the hexagonal crystalline structure of these a-plane GaN films.
Effect of the V/III ratio during buffer layer growth on the yellow and blue luminescence in undoped GaN epilayer has been studied by means of photoluminescence spectroscopy and high resolution X-ray diffraction.It is found that the densities of screw and edge threading dislocations increase with the V/III ratio of the buffer layer,and the intensities of the yellow luminescence(YL) and blue luminescence(BL) emissions also increase dramatically.However,the density ratio of the edge threading dislocation to the screw threading dislocation remains invariant,as well as the intensity ratio of YL emission to BL emission.It can be concluded from these phenomena that the edge threading dislocation and screw threading dislocation can enhance the YL and BL emissions,respectively.
InGaN films were deposited on(0001) sapphire substrates with GaN buffer layers under different growth temperatures by metalorganic chemical vapor deposition.The In-composition of InGaN film was approximately controlled by changing the growth temperature.The connection between the growth temperature,In content,surface morphology and defect formation was obtained by X-ray diffraction,scanning electron microscopy(SEM) and atomic force microscopy(AFM).Meanwhile,by comparing the SEM and AFM surface morphology images,we proposed several models of three different defects and discussed the mechanism of formation.The prominent effect of higher growth temperature on the quality of the InGaN films and defect control were found by studying InGaN films at various growth temperatures.
The influence of dry etching damage on the internal quantum efficiency of InGaN/GaN nanorod multiple quantum wells (MQWs) is studied.The samples were etched by inductively coupled plasma (ICP) etching via a selfassembled nickel nanomask,and examined by room-temperature photoluminescence measurement.The key parameters in the etching process are rf power and ICP power.The internal quantum efficiency of nanorod MQWs shows a 5.6 times decrease substantially with the rf power increasing from 3W to 100W.However,it is slightly influenced by the ICP power,which shows 30% variation over a wide ICP power range between 30W and 600W.Under the optimized etching condition,the internal quantum efficiency of nanorod MQWs can be 40% that of the as-grown MQW sample,and the external quantum efficiency of nanorod MQWs can be about 4 times that of the as-grown one.
We develop a model for the effect of thermal annealing on forming In-N clusters in GaInNP according to thermodynamics.The average energy variation for forming an In-N bond in the model is estimated according to the theoretical calculation.Using the model,the added number of In-N bonds per mol of InGaNP,the added number of nearest-neighbor In atoms per N atom and the average number of nearest-neighbor In atoms per N atom after annealing are calculated.The different function of In-N clusters in InGaNP and InGaN is also discussed,which is due to the different environments around the In-N clusters.
The quest for higher modulation speed and lower energy consumption has inevitably promoted the rapid development of semiconductor-based solid lighting devices in recent years. GaN-based light-emitting diodes (LEDs) have emerged as promising candidates for achieving high efficiency and high intensity, and have received increasing attention among many researchers in this field. In this paper, we use a self-assembled array-patterned mask to fabricate InGaN/GaN multi-quantum well (MQW) LEDs with the intention of enhancing the light-emitting efficiency. By utilizing inductively coupled plasma etching with a self-assembled Ni cluster as the mask, nanopillar arrays are formed on the surface of the InGaN/GaN MQWs. We then observe the structure of the nanopillars and find that the V-defects on the surface of the conventional structure and the negative effects of threading dislocation are effectively reduced. Simultaneously, we make a comparison of the photoluminescence (PL) spectrum between the conventional structure and the nanopillar arrays, achieved under an experimental set-up with an excitation wavelength of 325 mm. The analysis demonstrates that MQW-LEDs with nanopillar arrays achieve a PL intensity 2.7 times that of conventional LEDs. In response to the PL spectrum, some reasons are proposed for the enhancement in the light-emitting efficiency as follows: 1) the improvement in crystal quality, namely the reduction in V-defects; 2) the roughened surface effect on the expansion of the critical angle and the attenuated total reflection; and 3) the enhancement of the light-extraction efficiency due to forward scattering by surface plasmon polariton modes in Ni particles deposited above the p-type GaN layer at the top of the nanopillars.
The non-polar a-plane GaN is grown on an r-plane sapphire substrate directly without a buffer layer by metalorganic chemical vapour deposition and the effects of V/III ratio growth conditions are investigated. Atomic force microscopy results show that triangular pits are formed at a relatively high V/III ratio, while a relatively low V/III ratio can enhance the lateral growth rate along the c-axis direction. The higher V/III ratio leads to a high density of pits in comparison with the lower V/III ratio. The surface morphology is improved greatly by using a low V/III ratio of 500 and the roughness mean square of the surface is only 3.9 nm. The high resolution X-ray diffraction characterized crystal structural results show that the rocking curve full width at half maximum along the m axis decreases from 0.757 to 0.720 , while along the c axis increases from 0.220 to 0.251 with the V/III increasing from 500 μmol/min to 2000 μmol/min, which indicates that a relatively low V/III ratio is conducible to the c-axis growth of a-plane GaN.
In this paper,we simulate a new style vertical HVPE reactor by using computational fluid dynamics program FLUENT.In order to find the best parameter on the growth rate of Gallium nitride(GaN),we change the distance between the inlet and the substrate,GaCl and NH3 inlets,and also we add substrate rotation separately.With the increase of the distance between the substrate and the gas inlet,GaN deposition rate decreases and the uniformity becomes better.The results show that the optimal distance in this new-style vertical hydride vapour phase epitaxy(HVPE) system is 4 cm.Besides,as the distance between the GaCl inlet and the NH3 inlet changes,the uniformity of GaN deposition varies.Our findings indicate that the optimal distance is 3 cm.Furthermore,it is found that substrate rotation also affects the growth rate of GaN.
We have grown transition metal(Fe,Mn) doped GaN thin films on c-oriented sapphire by metal-organic chemical vapor deposition.By varying the flow of the metal precursor,a series of samples with different ion concentrations are synthesized.Microstructural properties are characterized by using a high-resolution transmission electron microscope.For Fe over-doped GaN samples,hexagonal Fe_3N clusters are observed with Fe_3N(0002) parallel to GaN(0002) while for Mn over-doped GaN,hexagonal Mn_6N_(2.58) phases are observed with Mn_6N_(2.58)(0002) parallel to GaN(0002).In addition,with higher concentration ions doping into the lattice matrix,the partial lattice orientation is distorted,leading to the tilt of GaN(0002) planes.The magnetization of the Fe over-doped GaN sample is increased,which is ascribed to the participation of ferromagnetic iron and Fe_3N.The Mn over-doped sample displays very weak ferromagnetic behavior,which probably originates from the Mn_6N_(2.58).
