Z. G. Xing

White light-emitting diodes based on a single InGaN emission layer

White light-emitting InGaN∕GaN diode with an InGaN underlying layer grown on the (0001) sapphire substrate was fabricated by low pressure metal-organic vapor phase epitaxy. The electroluminescence measurements show that the emitted white light is composed of blue and yellow lights, centered at around 440 and 570nm, respectively, for an injection current of 20mA. Cross-sectional transmission electron microscopy reveals that In-rich quantum dots were formed in InGaN wells due to phase separation of indium. It is suggested that the yellow and blue lights come from In-rich quantum dots and the low-indium regions, respectively, in InGaN quantum wells.

Effects of barrier growth temperature ramp-up time on the photoluminescence of InGaN∕GaN quantum wells

The influence of ramp-up time of barrier growth temperature on optical properties is investigated for InGaN∕GaN quantum wells deposited on sapphire substrate by metal organic chemical vapor deposition. Three ramp-up times are used from the low and high growth temperatures for the well and barrier, respectively. The results indicate that increasing the ramp-up time leads to a blueshift of the photoluminescence (PL) peak position and a broadening of the PL emission linewidth. Similarly, “S-shaped” temperature dependences of the PL peak energy are observed in all the samples. However, very different temperature dependences of PL linewidth, such as the conventional shaped, “U-shaped,” and S-shaped, are observed in the samples with different ramp-up time. These effects are attributed to the redistribution of the In-rich clusters in the wells. Small quantum-dot-like In-rich clusters with high density are considered to be formed in the wells for the sample with a long ramp-up time, leading to the unconventional ...

Control performance of a single-chip white light emitting diode by adjusting strain in InGaN underlying layer

Light emission from green to white in a single-chip light emitting diode is modulated by adjusting the strain in InGaN underlying layer (UL) embedded below an active layer of InGaN/GaN multiple quantum wells. Transmission electron microscopy combined with x-ray reciprocal space mapping reveals that indium phase separation in InGaN quantum well active layer is enhanced by using a partly relaxed InGaN UL and In-rich quantum dots with different size and indium composition are formed. They emit multicolor lights whose mixing produces white light. Quality of the white light could be controlled by modulation on relaxation degree of the InGaN UL.

Anomalous tunneling effect on photoluminescence of asymmetric coupled double InGaN/GaN quantum wells

Tunneling-assisted carrier transfer in coupled double InGaN∕GaN quantum wells (QWs) has been studied by temperature-dependent photoluminescence (PL) at varied excitation density. It is found that the carriers captured by the wide (“deep”) well are efficiently transferred to the adjacent narrow (“shallow”) one by resonant tunneling, which results in anomalous temperature dependence of PL intensity and significantly enhanced luminescent efficiency for the narrow well. This is disparate from those conventional tunneling-assisted behaviors in coupled double QWs constructed by zinc-blende materials without polarization effect, where the carriers are always tunneling from the narrow (“shallow”) well to the wide (“deep”) one.

High-quality GaNAs∕GaAs quantum wells with light emission up to 1.44μm grown by molecular-beam epitaxy

High-quality GaNAs/GaAs quantum wells with high substitutional N concentrations, grown by molecular-beam epitaxy, are demonstrated using a reduced growth rate in a range of 0.125-1 mu m/h. No phase separation is observed and the GaNAs well thickness is limited by the critical thickness. Strong room-temperature photoluminescence with a record long wavelength of 1.44 mu m is obtained from an 18-nm-thick GaN0.06As0.94/GaAs quantum well

Investigation on Photoluminescence Blue Shift of InGaN/GaN Quantum Wells Induced by Surface Band Bending

The effects of GaN cap layer thickness and doping type on photoluminescence (PL) are investigated for InGaN/GaN quantum wells (QWs), which are deposited on a C-plane sapphire substrate by metal organic chemical vapor deposition (MOCVD). As for the results, the QWs capped with an unintentional doped (un-doped) GaN layer show a linear PL blue shift behavior with decreased cap layer thickness, while for the QWs capped with a heavy n- or p-doped GaN layer none of the similar behaviors are observed until the cap layer is less than 25 nm. These phenomena are well explained by introducing the effects of upward surface band bending. Surface polarization discontinuity and surface states are considered as the origins of the surface band bending. Furthermore, the actual surface band bending value of the un-doped GaN is also extracted as Eb = 1.54 ±0.08 eV from the linear PL blue shift behavior.