R. Fehse

A quantitative study of radiative, Auger, and defect related recombination processes in 1.3-/spl mu/m GaInNAs-based quantum-well lasers

By measuring the spontaneous emission (SE) from normally operating /spl sim/1.3-/spl mu/m GaInNAs-GaAs-based lasers we have quantitatively determined the variation of each of the current paths present in the devices as a function of temperature from 130 K to 370 K. From the SE measurements we determine how the current I close to threshold, varies as a function of carrier density n, which enables us to separate out the main current paths corresponding to monomolecular (defect-related), radiative or Auger recombination. We find that defect-related recombination forms /spl sim/55% of the threshold current at room temperature (RT). At RT, radiative recombination accounts for /spl sim/20% of I/sub th/ with the remaining /spl sim/25% being due to nonradiative Auger recombination. Theoretical calculations of the threshold carrier, density as a function of temperature were also performed, using a ten-band k /spl middot/ p Hamiltonian. Together with the experimentally determined defect-related, radiative, and Auger currents we deduce the temperature variation of the respective recombination coefficients (A, B, and C). These are compared with theoretical calculations of the coefficients and good agreement is obtained. Our results suggest that by eliminating the dominant defect-related current path, the threshold current density of these GaInNAs-GaAs-based devices would be approximately halved at RT. Such devices could then have threshold current densities comparable with the best InGaAsP/InP-based lasers with the added advantages provided by the GaAs system that are important for vertical integration.

Theoretical and experimental analysis of 1.3-/spl mu/m InGaAsN/GaAs lasers

We present a comprehensive theoretical and experimental analysis of 1.3-/spl mu/m InGaAsN/GaAs lasers. After introducing the 10-band k /spl middot/ p Hamiltonian which predicts transition energies observed experimentally, we employ it to investigate laser properties of ideal and real InGaAsN/GaAs laser devices. Our calculations show that the addition of N reduces the peak gain and differential gain at fixed carrier density, although the gain saturation value and the peak gain as a function of radiative current density are largely unchanged due to the incorporation of N. The gain characteristics are optimized by including the minimum amount of nitrogen necessary to prevent strain relaxation at the given well thickness. The measured spontaneous emission and gain characteristics of real devices are well described by the theoretical model. Our analysis shows that the threshold current is dominated by nonradiative, defect-related recombination. Elimination of these losses would enable laser characteristics comparable with the best InGaAsP/InP-based lasers with the added advantages provided by the GaAs system that are important for vertical integration.

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.

A comparison of the thermal stability of InGaAsP, AlGaInAs and GaInNAs quantum-well lasers for 1.3 /spl mu/m operation

We present the measured temperature dependence of InGaAsP, AlGaInAs, and GaInNAs-based QW lasers and discuss J/sub th/ and T/sub o/ in terms of the dominant recombination paths.

A theoretical analysis of the radiative current and its dependence on pressure in GaInNAs 1.3 /spl mu/m lasers

Summary form only given. We have shown that it is necessary to introduce a modified 10-band k.p Hamiltonian to describe the band dispersion in GaInN/sub x/As/sub l-x/, adding two spin-degenerate nitrogen states to the conventional 8-band k.p Hamiltonian to account for the band gap reduction and modified conduction band dispersion. We use the modified Hamiltonian here to undertake a theoretical analysis of gain as a function of carrier density and radiative current density in ideal 1.3 /spl mu/m GaInN/sub x/As/sub 1-x//GaAs QW structures. We then use the model to analyse recent experimental data on the variation of threshold current with pressure in a GaInNAs/GaAs laser structure.

Intrinsic temperature sensitivities of 1.3 /spl mu/m GaInNAs/GaAs, InGaAsP/InP and AlGaInAs/InP-based semiconductor lasers

The apparent temperature stability of GaInNAs-based lasers is attributed to significant defect current. By removing this current, GaInNAs devices have a similar temperature dependence to InGaAsP devices whilst AlGaInAs devices are more thermally stable.

Carrier recombination processes in MOVPE and MBE grown 1.3 μm GaInNAs edge emitting lasers

By measuring the spontaneous emission (SE) from metal organic vapour phase epitaxy (MOVPE) grown ∼1.3 μm GaInNAs/GaAs-based lasers during normal operation, we have quantitatively determined the variation of each of the current paths present in the devices as a function of temperature from 130 to 370 K and compared these with results previously obtained for molecular beam epitaxy (MBE) grown GaInNAs lasers. From the SE measurements we determine how the current, I, close to threshold, varies as a function of carrier density, n, which enables us to separate out the main current paths corresponding to monomolecular (defect-related), radiative or Auger recombination respectively. We find that at room temperature (RT), defect-related recombination contributes ∼360 A/cm2 (MBE) and ∼565 A/cm2 (MOVPE) to the total current density at threshold. Radiative recombination accounts for ∼110 A/cm2 (MBE) and 195 A/cm2 (MOVPE) of Jth with the remaining ∼180 A/cm2 (MBE) and 760 A/cm2 (MOVPE) are due to non-radiative Auger recombination. Our results suggest that a larger threshold carrier density in the MOVPE grown device in comparison to the MBE lasers, can reasonably explain the larger current densities of the different recombination processes at RT. We tentatively associate this with higher optical loss processes in the MOVPE grown material.

Experimental and theoretical analysis of the recombination processes in GaInNs 1.3 /spl mu/m lasers

By measuring the spontaneous emission from normally operating /spl sim/1.3 /spl mu/m GaInNAs/GaAs-based lasers we have quantitatively determined the variation of each of the current paths present in the devices as a function of temperature from 130 K to 370 K.

Investigation of Carrier Recombination Processes and Transport Properties in GaInAsN/GaAs Quantum Wells

It is shown that the dramatic changes in threshold current density with changing active region growth temperature in 1.3μm GaInNAs‐based lasers can be attributed almost entirely to changes in the defect related monomolecular recombination current in the optically active material. In addition, growth temperature dependent changes in the QW morphology are shown to have a significant influence on the transport properties of the structure.

Influence of growth temperature on defect density in 1.3/spl mu/m GaInNAs-based lasers

We show that the dramatic changes in threshold current density with changing active region growth temperature in 1.3 /spl mu/m GaInNAs-based lasers can be attributed nearly entirely to changes in the defect related monomolecular recombination current.