Boon-Siew Ooi

InGaAs/GaAs Quantum-Dot Superluminescent Diode for Optical Sensor and Imaging

We report on the design and fabrication of a novel wideband superluminescent diode (SLD) based on InGaAs/GaAs quantum-dot structure. In this device, we monolithically integrate a photon absorber section to suppress lasing action and optical feedback oscillation. The fabricated SLDs produce a close-to-Gaussian shaped spectrum centered at 1210 nm with a bandwidth of 135 nm. Spectral ripple as low as 0.3 dB has been measured

Group-III intermixing in InAs∕InGaAlAs quantum dots-in-well

We report selective postgrowth band gap tuning of InAs∕InGaAlAs quantum dots-in-well grown on InP substrate using impurity-free group-III intermixing. In contrast to most reported intermixing results, SixNy annealing cap results in a larger band gap blueshift than SiO2 annealing cap with a differential shift of 92nm after annealing at 800°C for 30s. Intermixing also results in large wavelength tuning from 1.6to1.37μm at room temperature, accompanied by luminescence linewidth reduction and intensity improvement. According to our theoretical model, we postulate that the unusual In(GaAl)As intermixing is governed by different interdiffusion rates of group-III atoms.

The Influence of Nonequilibrium Distribution on Room-Temperature Lasing Spectra in Quantum-Dash Lasers

We demonstrate the effect of nonequilibrium carrier distribution in a self-assembled InAs-InAlGaAs quantum-dash-in-well semiconductor lasers on InP substrate. The progressive changes of electroluminescence spectrum with increasing injections show the presence of localized photon reabsorption and lasing action from different dash ensembles at room temperature as opposed to that obtained in typical self-assembled quantum-dot lasers only at low temperature below 100 K.

Postgrowth band gap trimming of InAs∕InAlGaAs quantum-dash laser

The authors demonstrate the selective postgrowth band gap engineering and the fabrication of band gap tuned laser in InAs–InAlGaAs quantum-dash lasers grown on InP substrate. The process utilizes nitrogen implantation to induce local defects and to enhance the group-III intermixing rate spatially upon the thermal annealing. Compared with the as-grown laser, intermixed laser with wavelength shifted by 127nm shows a 36% reduction in threshold current density and produces a comparable slope of efficiency. The integrity of the intermixed material is retained suggesting that intermixing process paves way to planar, monolithic integration of quantum-dash-based devices.

A single-directional microcavity laser with microloop mirrors and widened medium realized with quantum-well intermixing

We describe a linear-geometry microcavity laser with microloops as end reflectors to achieve single-directional output. Finite-difference time-domain simulation is used to optimize the microloop mirror (MLM) performance and simulate the laser operation. We show that a single-directional microlaser with cavity length as small as 25 /spl mu/m can be realized. A method to obtain higher output power from the microlaser with widened gain medium (WGM) is discussed. An initial fabrication of the MLM-WGM laser with transparent MLM formed by quantum-well intermixing is presented. A low-lasing threshold of /spl sim/0.4 mA is achieved.

The Spectral Analysis and Threshold Limits of Quasi-Supercontinuum Self-Assembled Quantum Dot Interband Lasers

This paper presents a theoretical model to explain the quasi-supercontinuum interband emission from InGaAs/GaAs self-assembled semiconductor quantum dot lasers by accounting for both inhomogeneous and homogeneous optical gain broadening. The experimental and theoretical agreement of a room temperature (293 K) broadband laser emission confirms the presence of multiple-state lasing actions in highly inhomogeneous dot ensembles. The corresponding full-width half-maximum of the photoluminescence is 76 meV as opposed to those wideband lasing coverage at only low temperature (~60 K) from typical quantum dot lasers. A newly proposed change of homogeneous broadening with injection that occurs only in highly inhomogeneous quantum dot system is critical to account for the continuous wideband lasing but not the conventional ideas of carrier dynamics in semiconductor lasers. In addition, the analysis of threshold conditions reveals that broadband lasing only occurs when the energy spacing between quantized energy states is comparable to the inhomogeneous broadening of quantum-dot nanostructures. The study is important in providing a picture of this novel device and realization of broad lasing coverage for diverse applications, especially in the research field of short-pulse generation and ultra-fast phenomena in semiconductor quantum-dot laser.

A Temporal Coherence Study of Quantum-Dot/Dash Broadband Lasers and Superluminescent Diodes

The temporal coherence functions of InGaAs-GaAs quantum-dot (QD) and InAs-InGaAlAs quantum-dash (Qdash) superluminescent diodes (SLDs) and broadband laser diodes (BLDs) are reported. Using an optical fiber-based spectral interferometer, the fabricated devices were shown to yield low coherence lengths of 4.00-12.29 mum and 33.48-74.56 mum for SLD and BLD devices, respectively. In addition, there were negligible secondary coherencies indicating that these devices have the potential for use in low coherent interferometric systems.

Gain and alpha factor of intermixed InAs/InAlGaAs quantum-dash lasers

We study the optical gain and alpha factor of InAs/InAlGaAs quantum-dash lasers on InP substrate after being subjected to the postgrowth intermixing process. The intermixing was achieved using dielectric capping process that involves the deposition of dielectric film and subsequent rapid thermal annealing. Compared to the un-intermixed laser, we found that the intermixed lasers with a 93 nm bandgap blue-shift exhibit good material quality with improved differential gain and comparable alpha factor.

Quantum-well Intermixing using Ge-doped Sol-gel Derived Silica Encapsulant Layer

We report the intermixing enhancement using the Ge-doped sol-gel derived silica encapsulant layer in InGaAs/InGaAsP quantum-well laser structure. A bandgap shift of ∼64 nm has been observed from 16% Ge-doped silica capped sample at an annealing temperature of 630°C while the intermixing at the similar temperature can be effectively suppressed with the e-beam evaporated SiO 2 encapsulant layer. Using our theoretical model, nearly identical activation energy of 1.7±0.5 eV was obtained from the intermixed sample with Ge-doped silica. Similar intermixing enhancement holds for high Ge-content cap in the intermixed GaAs/AlGaAs quantum-wells related to Ga vacancy injection. We postulate that the dissimilarity in interdiffusion behavior between 0% and 16% Ge-doped silica capped sample is only attributed to the difference in the number of beneficial vacancies that involve in the intermixing process.