In this letter the authors present a comprehensive study of the threshold current and its temperature dependence in GaAsSb-based quantum well edge-emitting lasers for emission at 1.3 m. It is found that at room temperature, the threshold current is dominated by nonradiative recombination accounting for more than 90% of the total threshold current density. From high hydrostatic pressure dependence measurements, a strong increase in threshold current with pressure is observed, suggesting that the nonradiative recombination process may be attributed to electron overflow into the GaAs/ GaAsP barrier layers and, to a lesser extent, to Auger recombination. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2369649͔Lasers emitting close to 1.3 m are of considerable importance for the development of metro-area networks. 1Progress in this area has been hindered largely by the need to significantly reduce the cost of the laser module itself. The incumbent InGaAsP quantum well ͑QW͒ material system used to make such lasers suffers from two problems: Firstly, the fact that they are grown on InP makes it difficult to produce vertical cavity surface emitting lasers ͑VCSELs͒ which are vastly more cost effective but are better suited to GaAs substrates. Secondly, the devices are highly susceptible to temperature variations resulting in the need to incorporate sophisticated temperature control electronics into the package, leading to an order of magnitude increase in cost. Hence, there has been considerable effort devoted to the development of GaAs-based laser active regions which emit at 1.3 m. InAs quantum dots 2 and GaInNAs-based QWs have been the subject of extensive research. However, the properties of even the best quantum dot lasers are far from ideal, since their threshold current density increases quickly with temperature around room temperature due to nonradiative recombination resulting in a low characteristic temperature, T 0 ϳ 50 K ͓T 0 = ͑d ln I th / dT͒ −1 ͔, similar to that of standard 1.3 m QW based lasers.3 P-doped quantum dot lasers can exhibit very high T 0 values ͑even infinite over a narrow temperature range͒, but this is achieved at the expense of higher threshold currents compared with undoped devices.4 For GaInNAs-based QW lasers, it has been shown that even for the best 1.3 m devices available, approximately 50% of the threshold current at room temperature may be attributed to defect-related recombination. 5 The implications of this on long-term device stability have yet to be fully addressed. Another possibility is the use of GaAsSb/ GaAs QWs.6 Lasers based upon this material have been produced, 7 but little, if any, research has been undertaken to assess the carrier recombination and temperature dependent processes occurring in such devices. The aim of this letter is to consider the characteristics of GaAsSb/ GaAs-based edge-emitting lasers and to explore the potential of GaAsSb/ GaAs active regions for use in 1.3 m VCSELs.The devices in this study consist of a triple GaAs 0.9 P 0.1 / GaAs/ GaAs 0.7...

Abstract-The authors describe a straightforward experimental technique for measuring the facet temperature of a semiconductor laser under high-power operation by analyzing the laser emission itself. By applying this technique to 1-mm-long 980-nm lasers with 6-and 9-m-wide tapers, they measure a large increase in facet temperature under both continuous wave (CW) and pulsed operation. Under CW operation, the facet temperature increases from 25 C at low currents to over 140 C at 500 mA. From pulsed measurements they observe a sharper rise in facet temperature as a function of current ( 400 C at 500 mA) when compared with the CW measurements. This difference is caused by self-heating which limits the output power and hence facet temperature under CW operation. Under pulsed operation the maximum measured facet temperature was in excess of 1000 C for a current of 1000 mA. Above this current, both lasers underwent catastrophic optical damage (COD). These results show a striking increase in facet temperature under high-power operation consistent with the facet melting at COD. This is made possible by measuring the laser under pulsed operation.

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The wafer of a 760 nm vertical-cavity surface-emitting laser (VCSEL), designed for oxygen sensing up to high temperatures, is investigated using photomodulated reflectance (PR). By varying the angle of incidence, the VCSEL cavity mode (CM) wavelength is tuned through the positions of two excitonic quantum well (QW) transitions. The PR is also measured over a large temperature range to determine when the QW ground-state transition is tuned with the CM. When tuned, the QW/CM PR lineshape becomes anti-symmetric, as predicted by theory. This occurs at 388 K, where the CM and QW wavelengths coincide at 760.7 nm. It is also observed that when tuned, the CM width measured in the reflectance spectrum is maximised. Temperature dependent device studies are also conducted on a 760 nm edge-emitting laser containing a similar active region as the VCSEL. It is found that up to 250 K the device behaves ideally, with the threshold current being entirely due to radiative recombination. However, as the temperature increases, electron leakage into the indirect X-minima of the barrier and cladding layers becomes increasingly significant. At 300 K, approximately 25% of the threshold current is found to be attributed to electron leakage and this increases to 85% at 388 K. The activation energy for this leakage process is determined to be 255 ^5 meV, indicating that electron escape from the QWs into the X-minima of the barrier and/or cladding layers is chiefly responsible for the device's poor thermal stability. These results suggest that VCSELs containing this active region are likely to suffer significantly from carrier leakage effects.

We have analysed experimentally the temperature and pressure dependence of 980 nm high-power GaAs/AlGaAs/InGaAs semiconductor lasers in the temperature (T) range 80-350 K. Measurements of the threshold current and spontaneous emission allow us to study the underlying recombination occurring in the devices. We observe that up to ≈250 K the dominant recombination mechanism is radiative (J th ∝ T). Above this temperature there is a super-linear increase in threshold current and a resulting decrease in the characteristic temperature, T 0 (≈130 K at room temperature). Pressure measurements at room temperature allow us to differentiate between possible recombination processes. They show that leakage into the X minima accounts for only 0.1% of the total threshold current at atmospheric pressure and room temperature. We therefore conclude that Auger recombination is the cause of the super-linear increase in threshold current over the normal temperature range of operation.