G. Knowles

Quantifying the Effect of Indirect Carrier Leakage on Visible Al(GaInP) Lasers Using High Pressures and Low Temperatures

The extreme temperature sensitivity of the threshold current, I th , above room temperature in visible edge-emitting lasers (EELS) is investigated. From measurements as a function of temperature we find that I th is dominated by the radiative current, I Rad up to ∼230 K so I th I Rad as expected for an ideal device. However, above 230 K, I th increases sharply due to the onset of indirect carrier leakage which we calculate to be ∼20% of I th at room temperature at an emission wavelength of 672 nm. By 350 K it accounts for >70% of I th . The operating wavelength of the device can be reduced by applying pressure and then we observe that the leakage rapidly increases and at 655 nm it forms ∼70% of I th at room temperature. This gives rise to a significant deterioration in the light output characteristics and has important implications for producing high power EELS and VCSEL structures based upon Al(GaInP) at these shorter operating wavelengths.

Evaluating the continuous-wave performance of AlGaInP-based red (667 nm) vertical-cavity surface-emitting lasers using low-temperature and high-pressure techniques

By measuring visible AlGaAs/AlGaInP vertical-cavity surface-emitting lasers (VCSELs) and similar edge-emitting lasers (EELs) as a function of temperature and pressure, we study the contributions of electron leakage and gain-cavity detuning on the threshold current, Ith, of VCSELs. In the EELs, leakage accounts for ∼20%Ith at room temperature, rising to ∼70%Ith at 80u200a°C. Similarly, leakage accounts for almost all of the increase in the VCSEL Ith above −100u200a°C and limits the cw output power. At low temperature or high pressure, however, the VCSEL Ith increases sharply due to misalignment of the gain peak to the high-energy side of the cavity mode. Under normal operating conditions, carrier leakage has the greatest effect on the VCSELs with gain-cavity detuning only becoming important at very low temperatures.

Investigation of 1.3-/spl mu/m GaInNAs vertical-cavity surface-emitting lasers (VCSELs) using temperature, high-pressure, and modeling techniques

We have investigated the temperature and pressure dependence of the threshold current (I/sub th/) of 1.3 /spl mu/m emitting GaInNAs vertical-cavity surface-emitting lasers (VCSELs) and the equivalent edge-emitting laser (EEL) devices employing the same active region. Our measurements show that the VCSEL devices have the peak of the gain spectrum on the high-energy side of the cavity mode energy and hence operate over a wide temperature range. They show particularly promising I/sub th/ temperature insensitivity in the 250-350 K range. We have then used a theoretical model based on a 10-band k.P Hamiltonian and experimentally determined recombination coefficients from EELs to calculate the pressure and temperature dependency of I/sub th/. The results show good agreement between the model and the experimental data, supporting both the validity of the model and the recombination rate parameters. We also show that for both device types, the super-exponential temperature dependency of I/sub th/ at 350 K and above is due largely to Auger recombination.

Assessing the performance of visible (665 nm) vertical cavity surface emitting lasers using high pressure and low temperature techniques

The effects of carrier leakage and gain-cavity alignment on the temperature dependence of the threshold current (I th ) in visible vertical cavity surface emitting lasers (VCSELs) are investigated. In order to assess the two effects and the degree to which they couple we have performed pressure and temperature experiments on VCSELs and their equivalent edge emitting lasers (EEL). We have established that the peak of the gain moves with pressure at a rate of 72 meV GPa -1 more than three times the rate of 22 meV GPa -1 for the cavity mode. However, we show that over the temperature operating range carrier leakage into the indirect X-minima is the major contributor to an increased I th , nevertheless optimised gain-cavity alignment can lead to more stable operation.

Self-consistent modelling of oxide aperture visible vertical-cavity surface-emitting laser devices

A comprehensive model employing the beam propagation method for the study of oxide-confined visible vertical-cavity surface-emitting lasers is presented. In this model all the major physical processes including the current density distribution, the self-heating effect of the devices, the carrier lateral diffusion in quantum wells and optical field modes are considered consistently. The threshold properties are calculated and the results suggest that the optimum oxide aperture radius is between 5 and 6 μm to achieve maximum output power for a substrate at room temperature.

Gain-cavity alignment in efficient visible (660 nm) VCSELs studied using high pressure techniques

Visible (660 nm) vertical-cavity surface-emitting lasers (VCSELs) for polymer fibre applications are very sensitive to temperature fluctuations and structural errors. Two devices with a 3 meV wave length separation were studied. Significant differences in the output performance can be explained by the relative offset of the cavity mode and the peak of the gain spectrum. The different behaviour of the two devices as a function of hydrostatic pressure can be explained by the gain–cavity offset. Temperature and pressure both shift the offset, but self-heating means that the cw variation is not always as expected. Electron leakage also changes with both pressure and temperature, and in both cases its effect is dominant over the gain–cavity offset in determining the threshold current variation.

Integrated optical and electronic modeling of oxide-confined visible VCSELs

A comprehensive beam propagation method (BPM) for the modeling of oxide-confined visible emitting (665nm) vertical-cavity surface-emitting lasers (VCSELs) aimed at polymer optical fibre (POF) communications is presented. In this model all the major physical processes, including the current density distribution, the self-heating effect of the devices, the carrier lateral diffusion in quantum wells, and the optical field modes are considered self-consistently. Using the model, the current flow, carrier diffusion in the active quantum wells, and temperature distribution are calculated. The model indicates severe current crowding around the edge of the oxide aperture within the VCSEL. Using a simple function to describe the variation of optical gain with temperature and wavelength, the threshold properties, transverse modes and the optical output current-light characteristics are calculated. The simulation results are compare favorably with measurements.

The temperature and pressure dependence of 1.3 /spl mu/m GaInNAs vertical-cavity surface-emitting lasers (VCSELs)

We have modelled the temperature and pressure dependence of the threshold current of GaInNAs-based VCSELs and compared the results with measured data.

Optical investigation of recombination processes in GaInNAs, InGaAsP and AlGalnAs quantum-well lasers using hydrostatic pressure

The lasing-energy dependence of carrier-recombination in InGaAsP, AlGaInAs and GaInNAs 1.3 /spl mu/m lasers is compared. For the first time we measure spontaneous emission at high pressure.

Characterization of 1.3-um wavelength GaInNAs/GaAs edge-emitting and vertical-cavity surface-emitting lasers using low temperature and high pressure

By measuring the spontaneous emission from normally operating ~1.3um GaInNAs/GaAs-based lasers grown by MBE and by MOVPE we have quantitatively determined the variation of monomolecular (defect-related ~An), radiative (~Bn2) and Auger recombination (~Cn3) as a function of temperature from 130K to 370K. We find that A, B and C are remarkably independent of the growth method. Theoretical calculations of the threshold carrier density as a function of temperature were also performed using a 10 band k·p Hamiltonian from which we could determine the temperature variation of A, B and C. At 300K, A=11x10-8 sec-1, B=8x10-11 cm3 sec-1 and C= 6x10-29 cm6 sec-1. These are compared with theoretical calculations of the coefficients and good agreement is obtained. Our results suggest that by eliminating defect-related currents and reducing optical losses, the threshold current density of these GaInNAs/GaAs-based edge-emitting devices would be more than halved at room temperature. The results from studies of temperature and pressure variation of ~1.3um VCSELs produced by similar MBE growth could also be explained using the same recombination coefficients. They showed a broad gain spectrum and were able to operate over a wide temperature range.