InGaN/GaN triangular shaped multiple quantum wells (QWs) grown by grading In composition with time were adopted as an active layer of blue light-emitting diodes (LEDs). Compared to the LEDs with conventional rectangular QW structures, the triangular QW LEDs showed a higher intensity and a narrower linewidth of electrical luminescence (EL), a lower operation voltage, and a stronger light-output power. EL spectra of the triangular-QW-based LEDs also showed that the peak energy is nearly independent of the injection current and temperature, indicating that the triangular QW LED is more efficient and stable than the rectangular one.

Articles you may be interested inDiscrimination of local radiative and nonradiative recombination processes in an InGaN/GaN single-quantum-well structure by a time-resolved multimode scanning near-field optical microscopy Nonradiative recombination processes of carriers in InGaN/GaN probed by the microscopic transient lens spectroscopy Rev. Sci. Instrum. 74, 575 (2003);

Temperature-dependent Hall effect measurements on unintentionally doped n-type GaN epilayers show that, above room temperature, the Hall-mobility values of different samples vary parallel with each other with temperature. We demonstrate that this anomaly is mainly due to a conductive layer near the GaN/sapphire interface for thin samples with low carrier density. Through trapping electrons, threading edge dislocations (TEDs) debilitate the epilayer contribution in a two-layer mixed conduction model involving the epilayer and the near-interface layer. The trapping may, in part, explain low mobility and anomalous transport in pure GaN layers. Scattering by TEDs is important only at low temperatures.

Structural and optical properties of various shapes of quantum wells (QWs), including rectangular, triangular, trapezoidal, and polygonal ones are investigated. Photoluminescence (PL) measurements show that the highest light emission efficiency and the best reproducibility in the intensity and wavelength are obtained from trapezoidal QWs. The temperature dependence of PL spectra indicates the more localized nature of excitons in the trapezoidal QWs. A plan-view transmission electron microscopy shows that quantum dots (QDs) are formed inside the dislocation loop in trapezoidal QWs. The distribution of QDs in size and composition becomes more uniform with trapezoidal QWs than with rectangular QWs, leading to superior light-emission characteristics. It is suggested that QD engineering and dislocation control are possible, to some extent, by the modulation of the QW shape in InGaN/GaN-based light-emitting devices.

Deep-level defect-related optical properties of undoped n-type GaN grown by metalorganic chemical vapor deposition are investigated using photoluminescence (PL), optical absorption (OA), photoconductivity (PC), and persistent photoconductivity (PPC) measurements. From the temperature dependence of the PL and OA, we find that the yellow luminescence (YL) is due to shallow-to-deep donor recombination. PL, PC, and PPC results manifest a strong correlation in properties related to deep levels. Samples which emit YL exhibit a PC peak at 1.9 eV due to the photoionization of deep levels as well as to the persistent photoconductivity effect, whereas samples with no YL have no PC peak in the forbidden gap and no PPC at any photon energy, suggesting a common origin. Furthermore, two types of PPC behavior were observed depending on the sample quality: typical stretched exponential decay in relatively thick samples and photocurrent quenching and a subsequent reduction of the dark current in thin samples. An explanation of the latter phenomenon based on photoinduced metastable electron traps in a highly defective layer near the interface is suggested from the temporal behavior of the PC. These traps seem to disappear slowly after the illuminating light is turned off.