Hui Yang

Thermal annealing behaviour of Pt on n-GaN Schottky contacts

The structural evolution and temperature dependence of the Schottky barrier heights of Pt contacts on n-GaN epilayer at various annealing temperatures were investigated extensively by Rutherford backscattering spectrometry, x-ray diffraction measurements, Auger electron spectroscopy, scanning electron microscopy and current–voltage measurements. The temperature dependence of the Schottky barrier heights may be attributed to changes of surface morphology of Pt films on the surface and variation of nonstoichiometric defects at the interface vicinity. Experimental results indicated the degradation of Pt contacts on n-GaN above 600uC.

Nonlinear optical response and applications of tin disulfide in the near- and mid-infrared

Layered metal dichalcogenides (LMDs) have received considerable attention in optoelectronics and photonics. Tin disulfide (SnS2) as a member of the LMDs has been employed for transistors, energy storage, and photocatalysts. The optical properties of SnS2 in the ultraviolet and visible regions have been widely investigated, while the applications of SnS2 in the near- and mid-infrared regions are still rare. Here, we demonstrate the nonlinear optical response of layered SnS2 that is exploited as a saturable absorber in the near- and mid-infrared regions. The saturable absorption of SnS2 is measured at 1.06 and 1.55u2009μm, which illustrates a low saturable intensity. SnS2 covered on a D-shaped fiber is used to initiate the mode-locking operations in erbium-, ytterbium-, and thulium-doped fiber lasers and ultrafast pulses are achieved at 1.03, 1.56, and 1.91u2009μm. These results make SnS2 an appealing candidate for broadband applications across the near- and mid-infrared regions.

Investigation of InGaN/GaN laser degradation based on luminescence properties

Degradation of InGaN/GaN laser diode (LD) is investigated based on the luminescence properties. Gradual degradation of the LD is presented with the threshold current increase and the slope efficiency decrease. The cathodoluminescence and photoluminescence characterizations of the LD show a dislocation independent degradation of the active region under the ridge. Detailed studies on the temperature-dependent micro-photoluminescence and the electroluminescence indicate that the degradation of the LD is attributed to the generation of non-radiative recombination centers in the local multiple quantum well regions with lower indium content. The activation energy of the non-radiative recombination centers is about 10.2u2009meV.

Identification of degradation mechanisms of blue InGaN/GaN laser diodes

A comprehensive analysis of the degradation mechanism of blue InGaN/GaN laser diodes (LDs) is carried out by investigating the electrical and optical characteristics. The increase in the leakage current as well as decrease in the slope efficiency is observed. The luminescence properties of the active region at different aging stages are studied by means of cathodoluminescence. Significant degradation of the active region is observed on the room temperature cathodoluminescence while the low temperature cathodoluminescence shows almost no degradation, indicating that the degradation of the LDs is due to generation of low temperature frozen point defects. Furthermore, the generation of the defects follows a kinetic mechanism enhanced by electron-hole non-radiative recombination which explains the acceleration of time degradation in our LDs.

Injection current dependences of electroluminescence transition energy in InGaN/GaN multiple quantum wells light emitting diodes under pulsed current conditions

Injection current dependences of electroluminescence transition energy in blue InGaN/GaN multiple quantum wells light emitting diodes (LEDs) with different quantum barrier thicknesses under pulsed current conditions have been analyzed taking into account the related effects including deformation caused by lattice strain, quantum confined Stark effects due to polarization field partly screened by carriers, band gap renormalization, Stokes-like shift due to compositional fluctuations which are supposed to be random alloy fluctuations in the sub-nanometer scale, band filling effect (Burstein-Moss shift), and quantum levels in finite triangular wells. The bandgap renormalization and band filling effect occurring at high concentrations oppose one another, however, the renormalization effect dominates in the concentration range studied, since the band filling effect arising from the filling in the tail states in the valence band of quantum wells is much smaller than the case in the bulk materials. In order to c...

Hole transport in c-plane InGaN-based green laser diodes

Hole transport in c-plane InGaN-based green laser diodes (LDs) has been investigated by both simulations and experiments. It is found that holes can overflow from the green double quantum wells (DQWs) at high current density, which reduces carrier injection efficiency of c-plane InGaN-based green LDs. A heavily silicon-doped layer right below the green DQWs can effectively suppress hole overflow from the green DQWs.

Identification of Degradation Mechanisms Based on Thermal Characteristics of InGaN/GaN Laser Diodes

A method of identifying laser degradation mechanism is established based on thermal characteristic analysis of InGaN/GaN laser diodes (LDs). Both steady and transient thermal characteristics of LDs are calculated by the finite-element analysis method, the results show that thermal resistance and thermal time constant of each layer are determined by the corresponding structure and material. Experiments on thermal characteristics of LDs are carried out, degradation induced heat transport irregularities are localized by comparing the transient cooling curves of the virgin, and degraded LDs and further analyses give more information on degradation mechanisms of the LDs. The results confirm that this identification method is an effective method, which gives specific guidance for the analysis of the laser degradation mechanisms.

Deep centers in AlGaAs/GaAs GRIN-SCH SQW laser structures grown by MBE and MOCVD

CHINESE ACAD SCI,INST SEMICOND,LAB SEMICOND MAT SCI,NATL LAB SUPERLATTICES & MICROSTRUCT,BEIJING 100083,PEOPLES R CHINA

A low resistivity n++-InGaN/p++-GaN polarization-induced tunnel junction

A low resistivity n++-InGaN/p++-GaN tunnel junction is illustrated. The tunneling current density of tunnel junction with 30 percent In content in InGaN layer turns out to be extraordinary high (10 kA cm−2) even at a relatively low bias voltage (0.1 V) compared with traditional n++-GaN/p++-GaN. And we optimize the InGaN layer including the thickness, indium component and the doping concentration to increase the tunneling probability with the 1D Schrodinger Poisson self-consistent method and WKB (Wentzel-Kramers-Brillouin) approximation. It is shown that the peak value of electric field in tunnel junction caused by spontaneous polarization and piezoelectric effect reaches 7.1 MV cm−1 with the 2D hole gas concentration of 2 × 1020 cm−3 at the interface between InGaN and GaN. That indicates n++-InGaN/p++-GaN tunnel junction has a potential application in GaN-based optoelectronic device.