Guo Xia

Tunable Vertical-Cavity Surface-Emitting Lasers Integrated with Two Wafers

A novel two-wafer concept for micro-electro-mechanically tunable vertical cavity surface emitting lasers (VCSELs) is presented. The VCSEL is composed by two wafers: one micro-electromechanical-system membrane wafer with four arms to adjust the cavity length through electrostatic actuation and a “half-VCSEL wafer consisting of a fixed bottom mirror and an amplifying active region. The measurement results of the electricity pumped tunable VCSEL with more than 9 mW output power at room temperature over the tuning range prove the feasibility of the proposition.

A Flip-Chip AlGaInP LED with GaN/Sapphire Transparent Substrate Fabricated by Direct Wafer Bonding

A red-light AlGaInP light emitting diode (LED) is fabricated by using direct wafer bonding technology. Taking N-GaN wafer as the transparent substrate, the red-light LED is flip-chiped onto a structured silicon submount. Electronic luminance (EL) test reveals that the luminance flux is 130% higher than that of the conventional LED made from the same LED wafer. Current–voltage (I–V) measurement indicates that the bonding processes do not impact the electrical property of AlGaInP LED in the small voltage region (V 1.5 V), the I–V characteristic exhibits space-charge-limited currents characteristic due to the p-GaAs/n-GaN bonding interface.

Analysis of the operating point of a novel multiple-active-region tunneling-regenerated vertical-cavity surface-emitting laser

A novel multiple-active-region tunneling-regenerated vertical-cavity surface-emitting laser (VCSEL) with a greater-than-unity differential quantum efficiency is proposed. This novel VCSEL is expected to have an improved performance, specifically, reduced threshold current and heightened output power. The optimum reflectivity in terms of output power is determined for this novel VCSELs with fixed supply current and series resistance as a parameter. We compare the output power of the novel structure with that of the traditional structure at the same reflectivity and injected current. Also, we compare the threshold current of the novel structure with that of the traditional structure at the same reflectivity and output power. Finally, we prove the advantage of the novel structure in theory.

Polarization-Stable 980nm Vertical-Cavity Surface-Emitting Lasers with Diamond-Shaped Oxide Aperture*

Polarization-stable 980nm oxide-confined vertical-cavity surface-emitting lasers with 3 μm diamond-shaped aperture are fabricated by comprehensively utilizing the anisotropic properties of wet etching and wet nitrogen oxidation of III–V semiconductor materials. Polarization-stable operation along the major axis of the diamond-shaped oxide aperture with 11 dB orthogonal polarization suppression ratio is achieved in a temperature range of 15–55°C from the threshold to 4 mA.

The scalability of the tunnel-regenerated multi-active-region light-emitting diode structure

The scalability of the tunnel-regenerated multi-active-region (TRMAR) structure has been investigated for the application in light-emitting diodes (LEDs). The use of the TRMAR structure was proved theoretically to have unique advantages over conventional single-active-layer structures in virtually every aspect, such as high quantum efficiency, high power and low leakage. Our study showed that the TRMAR LED structure could obtain high output power under low current injection and high wall-plug efficiency compared with the conventional single-active-layer LED structure.

GaAs backside via-hole etching using ICP system

A high etch rate GaAs via-hole process was studied in an inductively coupled plasma system using Cl2/BCl3 gas system. The effects of process parameters on the GaAs etch rate were investigated. The influences of photoresist SiO2 and Ni masks on the resultant profiles were also studied by scanning electron microscopy. A maximum etch rate of 8.9 μm/min was obtained and the etched profiles were optimized.

Strain Field in GaAs/GaN Wafer-Bonding Interface and Its Microstructure

The strain fields in a wafer-bonded GaAs/GaN structure are measured by electron backscatter diffraction (EBSD). Image quality (IQ) of EBSD Kikuchi patterns and rotation angles of crystal lattices as strain sensitive parameters are employed to characterize the distortion and the rotation of crystal lattices in the GaAs-interface-GaN structure, as well as to display the strain fields. The results indicate that the influence region of the strains in the wafer-bonded GaAs/GaN structure is mainly located in GaAs side because the strength of GaAs is weaker than that of GaN. The cross-sectional image of transmission electron microscopy (TEM) further reveals the distortion and the rotation of crystal lattices induced by strains systematically.

Micromechanical tunable vertical-cavity surface-emitting lasers

We report the study on a short wavelength-tunable vertical-cavity surface-emitting laser utilizing a monolithically integrated bridge tuning microelectromechanical system. A deformable-bridge top mirror suspended above an active region is utilized. Applied bridge-substrate bias produces an electrostatic force which reduces the spacing of air-gap and tunes the resonant wavelength toward a shorter wavelength (blue-shift). Good laser characteristics are obtained: such as continuous tuning ranges over 11 nm near 940 nm for 0–9 V tuning bias, the peak output power near 1 mW and the full-width-half-maximum limited to approximately 3.2–6.8 nm. A detailed simulation of the micromechanical and optical characteristics of these devices is performed, and the ratio of bridge displacement to wavelength shift has been found to be 3:1.

Phosphor-free white light-emitting diodes*

The multiple color-matching schemes that could improve the color rendering index for phosphor-free white LEDs are discussed. Then we review a few of the recent research directions for phosphor-free white LEDs, which include the development of monolithic GaN-based white LEDs and hybrid integrated GaN-based and AlGaInP-based white LEDs. These development paths will pave the way toward commercial application of phosphor-free white LEDs in the coming years.

Optimal oxide-aperture for improving the power conversion efficiency of VCSEL arrays

The maximum power conversion efficiencies of the top-emitting, oxide-confined, two-dimensional integrated 2×2 and 4×4 vertical-cavity surface-emitting laser (VCSEL) arrays with the oxide-apertures of 6 μm, 16 μm, 19 μm, 26 μm, 29 μm, 36 μm, 39 μm, and 46 μm are fabricated and characterized, respectively. The maximum power conversion efficiencies increase rapidly with the augment of oxide-aperture at the beginning and then decrease slowly. A maximum value of 27.91% at an oxide-aperture of 18.6 μm is achieved by simulation. The experimental data are well consistent with the simulation results, which are analyzed by utilizing an empirical model.