GaSb Material System Research Articles

Diode-pumped 88 fs SESAM mode-locked Tm,Ho:CLNGG laser at 2090 nm

We report on a passively mode-locked Tm,Ho:CLNGG laser operating at 2090 nm, pumped by a multimode fiber-coupled 793 nm laser diode, representing the first demonstration of a diode-pumped sub-100-fs mode-locked laser at 2.1 μm wavelength. Due to the disordered nature of the gain material that exhibits a broad and smooth gain profile, pulses as short as 88 fs were achieved with an average output power of 120 mW at a repetition rate of 70.3 MHz. Stable self-starting mode-locked operation was obtained using a semiconductor saturable absorber mirror based on the GaSb material system.

Full optical SESAM characterization methods in the 1.9 to 3-µm wavelength regime.

Semiconductor saturable absorber mirrors (SESAMs) are widely used for modelocking of various ultrafast lasers. The growing interest for SESAM-modelocked lasers in the short-wave infrared and mid-infrared regime requires precise characterization of SESAM parameters. Here, we present two SESAM characterization setups for a wavelength range of 1.9 to 3 µm to precisely measure both nonlinear reflectivity and time-resolved recovery dynamics. For the nonlinear reflectivity measurement, a high accuracy (<0.04%) over a wide fluence range (0.1-1500 µJ/cm2) is achieved. Time-resolved pump-probe measurements have a resolution of about 100 fs and a scan range of up to 680 ps. Using the two setups, we have fully characterized three different GaSb-SESAMs at an operation wavelength of 2.05 µm fabricated in the FIRST lab at ETH Zurich. The results show excellent performance suitable for modelocking diode-pumped solid-state and semiconductor disk lasers. We have measured saturation fluences of around 4µJ/cm2, modulation depths varying from 1% to 2.4%, low non-saturable losses (∼ 0.2%) and sufficiently fast recovery times (< 32 ps). The predicted influence of Auger recombination in the GaSb material system is also investigated.

Single mode GaSb diode lasers for sensor applications in a long wavelength regime

The wavelength, λ, range of 1.8 μm≤λ≤3.5 μm contains strong spectral absorption lines of many gases used in health, industry, safety, and medicine and whose sensitive and quantitative detection is desirable. However, the performance of InP diode lasers markedly deteriorates beyond λ∼2 μm. In this paper we present new results on developing tunable high power single mode laser diodes based on the GaSb material system with emission in the wavelength range of 1.8 μm≤λ≤2.2 μm.

Molecular beam epitaxy on gas cluster ion beam-prepared GaSb substrates: Towards improved surfaces and interfaces

A key problem in producing mid-infrared optoelectronic and low-power electronic devices in the GaSb material system is the lack of substrates with appropriate surfaces for epitaxial growth. Chemical mechanical polishing (CMP) of GaSb results in surface damage accompanied by tenacious oxides that do not easily desorb. To overcome this, we have developed a process using gas cluster ion beams (GCIB) to remove surface damage and produce engineered surface oxides. In this paper, we present surface modification results on GaSb substrates using O2-, CF4/O2-, and HBr-GCIB processes. X-ray photoelectron spectroscopy of GCIB produced surface layers showed the presence of mixed Ga- and Sb-oxides, with mostly Ga-oxides at the interface, desorbing at temperatures ranging 530°C to 560°C. Cross-sectional transmission electron microscopy of molecular beam epitaxy grown GaSb/AlGaSb layers showed that GCIB surfaces yielded smooth defect free substrate to epi transitions as compared to CMP surfaces. Furthermore, HBr-GCIB surfaces exhibited neither dislocation layers nor discernable interfaces, indicating complete oxide desorbtion prior to epigrowth on a clean single crystal template. Atomic force microscopy of GCIB epilayers exhibited smooth surfaces with characteristic step-terrace formations comprising monatomic steps and wide terraces. The HBr-GCIB process can be easily adapted to a large scale manufacturing process for epi-readymore » GaSb.« less

GaSb-based lasers with two-dimensional photonic crystal mirrors

We present the realization of two-dimensional (2D) photonic crystals (PhCs) on the GaSbmaterial system. An electron cyclotron resonance reactive ion etch process usingCl2/Ar allows the fabrication of PhCs covering air fill factors off = 20%–50%, latticeperiods of a = 400–500 nm and aspect ratios of 5:1. Quality and reflectivity of these structuresare evaluated by incorporating the PhCs as high reflective back mirrors inGaSb-based ridge waveguide lasers with cavity lengths between 200 and1100 µm with thefront facet as cleaved. The shortest devices show remarkable threshold currents below 12 mA and efficienciesof 0.23 W A−1, yielding a maximum output power of almost 19 mW, proving the applicability of thechosen approach to numerous further concepts based on 2D PhCs on the GaSb materialsystem.

Internal cooling in a semiconductor laser diode

A thermal model of a diode laser structure is developed which includes a bipolar thermoelectric term not included in previous models. It is shown that heterostructure band offsets can be chosen so that there are thermoelectric cooling sources near the active region; this method of cooling is internal to the device itself, as opposed to temperature stabilization schemes which employ an external cooler. A novel laser structure is proposed that is capable of internal cooling in the Ga/sub 1-x/In/sub x/As/sub y/Sb/sub 1-y/-GaSb material system with /spl lambda/ = 2.64 /spl mu/m.

Resonant cavity-enhanced (RCE) photodetector based on Ga(In)Sb for gas-sensing applications

Resonant cavity-enhanced (RCE) detectors based on the GaSb material system have been demonstrated for the first time. Calculations show that there is a four-fold increase in the external quantum efficiency for an RCE detector over a conventional non-resonant structure. The back mirror is formed by an 18-period GaAs/AlAs quarter-wave stack with the front reflector being the air-semiconductor interface and the absorber region being bulk GaSb. Optical spectra show the resonant wavelength to be at 1748 nm and the observed enhancement in the photocurrent shows a four-fold increase over a non-resonant structure.