Chi Sun Kim

Formation mechanism of V defects in the InGaN/GaN multiple quantum wells grown on GaN layers with low threading dislocation density

V-defect formation of the InxGa1−xN/GaN multiple quantum wells (MQWs) grown on GaN layers with different threading dislocation (TD) densities was investigated. From cross-sectional transmission electron microscopy, we found that all V defects are not always connected with TDs at their bottom. By increasing the indium composition in the InxGa1−xN well layer or decreasing the TD density of the thick GaN layer, many V defects are generated from the stacking mismatch boundaries induced by stacking faults which are formed within the MQW due to the strain relaxation. Also, TD density in the thick GaN layer affects not only the origin of V-defect formation but also the critical indium composition of the InxGa1−xN well on the formation of V defects.

Effect of growth interruptions on the light emission and indium clustering of InGaN/GaN multiple quantum wells

InGaN/GaN multiple quantum wells (MQWs) grown with various growth interruptions between the InxGa1−xN well and GaN barrier by metalorganic chemical vapor deposition were investigated using photoluminescence (PL), high-resolution transmission electron microscopy, and energy filtered transmission electron microscopy (EFTEM). The integrated PL intensity of the MQWs with growth interruptions is abruptly reduced compared to that of the MQW without growth interruption. Also, as the interruption time increases the peak emission shows a continuous blueshift. Evidence of indium clustering is directly observed both by using an indium ratio map of the MQWs and from indium composition measurements along an InGaN well using EFTEM. The higher-intensity and lower-energy emission of light from the MQW grown without interruption showing indium clustering is believed to be caused by the recombination of excitons localized in indium clustering regions and the increased indium composition in these recombination centers.

Microstructural characterization of InGaN/GaN multiple quantum wells with high indium composition

Abstract 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 V-defects 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).

Spatial variation of photoluminescence and related defects in InGaN/GaN quantum wells

Spatially and spectrally resolved photoluminescence of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition is studied with near-field scanning optical microscopy (NSOM) and transmission electron microscopy (TEM). High-spatial-resolution NSOM images show bright blue quantum well emission around V defects and yellow emission inside the defects. TEM data suggest that the spatial distribution of blue luminescence is partly due to dislocation gettering by V defects. The yellow emission is attributed to the Ga vacancy-impurity complexes trapped inside V defects.

Effects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition

Effects of growth interruption on the optical and the structural properties of InGaN/GaN quantum wells were investigated by using photoluminescence, transmission electron microscopy, optical microscopy, and high resolution x-ray diffraction. The InxGa1−xN/GaN (x>0.2) quantum wells used in this study were grown on c-plane sapphire by using metalorganic chemical vapor deposition. The interruption was carried out by closing the group-III metalorganic sources before and after the growths of the InGaN quantum well layers. The transmission electron microscopy images show that with increasing interruption time, the quantum-dot-like regions and well thickness decreased due to indium reevaporation or the thermal etching effect. As a result the photoluminescence peak position was blueshifted and the intensity was reduced. Temperature- and excitation-power-dependent photoluminescence spectra support the results of transmission electron microscopy measurements. The sizes and the number of V defects did not differ wit...

Strong acceptor density and temperature dependences of thermal activation energy of acceptors in a Mg-doped GaN epilayer grown by metalorganic chemical-vapor deposition

P-type GaN layers were grown on sapphire by metalorganic chemical-vapor deposition and then rapid thermal annealing (RTA) was performed to electrically activate Mg impurities. Varied acceptor densities were obtained by RTA temperature and Mg concentration. Temperature-dependent Hall effects show that the thermal activation energy of the acceptor (EA) is strongly dependent on the acceptor density (NA), approximated by EA(0)=372−1.16×10−18 NA meV at 0 K. A strong temperature dependence of EA was also obtained in this study.

Effect of compressive strain relaxation in GaN blue light-emitting diodes with variation of n+‐GaN thickness on its device performance

The effects of compressive strain relaxation with increasing n‐GaN thickness on device performances of GaN blue light-emitting diodes (LEDs) were investigated. It was found that the compressive strain relaxation in LEDs with thicker n‐GaN occurred more considerably, following by the growth of active layer and p‐GaN, and generated many stacking faults right beneath the InGaN active layer, which might be related to a decrease of the LED output power. On the contrary, the LED photoluminescence intensity increased surprisingly with n‐GaN thickness. It was understood that the compressive strain relaxation enhanced localized states in InGaN wells.

Structural and optical characteristics of InGaN/GaN multiple quantum wells with different growth interruption

InGaN/GaN multiple quantum wells (MQWs) grown with various growth interruptions between InGaN well and GaN barrier by metalorganic chemical vapor deposition were investigated using photoluminescence, high-resolution transmission electron microscopy (HRTEM), and energy filtered transmission electron microscopy (EFTEM). The luminescence intensity of the MQWs with growth interruptions is abruptly reduced compared to that of the MQW without growth interruption. Also, as the interruption time increases the peak emission shows a continuous blue shift. We found that the higher intensity and lower energy emission of the MQW grown without interruption is caused by the recombination of excitons localized from indium clustering regions. Evidence of indium clustering is directly observed by indium ratio map of MQWs and indium composition measurements along an InGaN well using EFTEM.

Structural properties of GaN grown by pendeo-epitaxy with In-doping

We have studied the effect of isoelectronic In-doping on the structural properties of GaN grown by pendeo-epitaxy. From an analysis of cross-sectional transmission electron microscopy (TEM) images, the threading dislocation originating from the (0001) facet of GaN seed layer, thereafter propagating onto the top surface of regrown GaN layer, were reduced due to isoelectronic In-doping, which could enhance vacancy trapping. In addition, threading dislocations in the coalescence region were not observable. These results indicate that these dislocations are bent or terminated in the boundary of coalesced region. Also, the crystalline quality was improved from the results of high resolution X-ray diffraction and TEM measurements.

Co-doping characteristics of Si and Zn with Mg in p-type GaN

The authors investigated the doping characteristics of Mg doped, Mg-Si co-doped, and Mg-Zn co-doped Gan films grown by metalorganic chemical vapor deposition. They have grown p-GaN film with a resistivity of 1.26 {center_dot} cm and a hole density of 4.3 x 10{sup 17} cm{sup {minus}3} by means of Mg-Si co-doping technique. The Mg-Si co-doping characteristic was also explained effectively by taking advantage of the concept of competitive adsorption between Mg and Si during the growth. For Mg-Zn co-doping, p-GaN showing a low electrical resistivity (0.7 {center_dot} cm) and a high hole concentration (8.5 x 10{sup 17} cm{sup {minus}3}) was successfully grown without the degradation of structural quality of the film. Besides, the measured specific contact resistance for Mg-Zn co-doped GaN film is 5.0 x 10{sup {minus}4} {center_dot} cm{sup 2}, which is lower value by one order of magnitude than that for only Mg doped GaN film (1.9 x 10{sup {minus}3} {center_dot} cm{sup 2}).