The photoluminescence investigation at a low temperature was carried out in In0.13Ga0.87N/GaN single quantum well (SQW) and multiple quantum wells with 10 (10QW) or 5 periods. With decreasing number of wells, the emission peak shows a redshift. In the case of a low excitation power, the emission intensity is enhanced by an increase in the number of wells while it decreases in the case of a high excitation power. With increasing excitation power, the emission peak of the SQW exhibits a blueshift and its linewidth decreases, but the emission peak of the 10QW remains unchanged and its linewidth increases. Based on the theory of the quantum confined Stark effect, the behavior of the SQW and the 10QW can be well explained. This result should be highly emphasized in designing InGaN/GaN based optical devices.
Photoluminescence spectra of GaN grown by metalorganic chemical-vapor deposition on sapphire show that by reactive ion etching, the intensity of the yellow luminescence (YL) band decreases compared to that of the as-grown GaN, due to nonradiative recombination at the damage-induced defect centers. The intensity of the YL in dry-etched GaN has been found to be dependent on rf power and postetch annealing. No change in intensity is observed with further etching indicating a uniform spread of yellow emitters in the epilayer which supports the view that point defects like VGa are the origin of the YL.
SUMMARY Internal quantum efficiency (IQE) is usually estimated from temperature dependence of photoluminescence (PL) intensity by assuming that the IQE at cryogenic temperature is unity. III-nitride samples, however, usually have large defect density, and the assumption is not necessarily valid. In 2016, we proposed a new method to estimate accurate IQE values by simultaneous PL and photo-acoustic (PA) measurements, and demonstratively evaluated the IQE values for various GaN samples. In this study, we have applied the method to InGaN quantum-well active layers and have estimated the IQE values and their excitation carrier-density dependence in the layers. key words: internal quantum efficiency, recombination, PAS, PL
Effect of dry etching conditions on surface morphology and optical properties of GaN films in chlorine-based inductively coupled plasmasReactive ion etching of GaN has been carried out in two different plasma chemistries using 10Cl 2 /10Ar and 1CH 4 /9Cl 2 /10Ar at various applied radio frequency ͑rf͒ power. We have addressed the postetch surface characteristics of GaN, and the effect of CH 4 addition to chlorine plasma and the variation of rf power are discussed. Surface contamination, roughness, and stoichiometry have been determined from the results of secondary ion mass spectrometry. It is observed that in the case of plasma with 5% CH 4 , above 125 W, contamination of carbon is minimal and roughness is similar to that of the as-grown sample. At rf power less than 125 W, the Ga/N ratio of the etched surface is almost unity, whereas at rf power more than 125 W, it is more than unity. When the GaN surface is etched with only chlorine plasma, the surface is Ga excess at all rf power applied. The intensity of the main band-to-band photoluminescence peak is found to decrease when 10Cl 2 /10Ar is used, and the intensity was a minimum at 200 W. When 5% CH 4 is added to the plasma, the intensity at 200 W became almost the same as that of the as-grown sample, indicating minimal damage induced in the surface.
In order to make a precise determination of InGaN material parameters (valence-band A parameters and deformation potentials), reported experimental data on polarization properties have been analyzed by the kÁp perturbation theory, in which we utilized fact that the polarization properties are sensitive to the material parameters. It is found that the polarization properties are largely affected by the deformation potentials while the valence-band A parameters have small effects. In addition, it is found that two deformation potentials' sets roughly fit with the reported experimental data. From the calculation using these two parameters' sets, it is predicted that low-angle semipolar substrate orientation (u ¼ 308-408) are promising for low-cost and high-performance green laser diodes with cleaved facet cavity mirrors. These results support our previous prediction based on analytical calculations. 1 Introduction Utilization of InGaN quantum wells (QWs) on non-c-crystal planes for active layers of green laser diodes (LDs) has attracted attention, because internal electronic field can be reduced in the QWs [1]. In these structures, in-plane optical anisotropy appears, and optical gain is concentrated into one particular direction. Thus, the optical polarization properties have to be considered for the structural design of laser devices. In general, there are two bands at the top of the valence bands in InGaN material system, and one of them has X 1 -like character and the other has X 2 -like, where the X 1 direction is the normal direction to the c-axis on the substrate plane, and the X 2 direction is the projection of the c-axis on the substrate plane, as shown in Fig. 1(a). Polarization properties are mainly determined by the energy difference (DE) between X 1 -and X 2 -like bands shown in Fig. 1(b). Thus, the value of DE can be an index of the polarization properties (e.g., positive sign of DE means that emission is polarized in the X 1 direction). In our previous paper, we reported that these polarization properties are dependent on the substrate orientations and QW
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