On the thermal stability of 1.3μm GaAsSb/GaAs-based lasers

In spite of the almost ideal variation of the radiative current of 1.3μm GaAsSb/GaAs-based lasers, the threshold current, Jth, is high due to non-radiative recombination accounting for 90% Jth near room temperature. This also gives rise to low To values ~60K close to room temperature, similar to that for InGaAsP/InP. GaAs-based vertical cavity surface emitting lasers (VCSELs) emitting close to 1.3μm are of considerable importance for the development of metro-area networks. There has been considerable effort devoted to the development of high quality GaAs based laser active regions which emit at 1.3μm. InAs quantum dots and GaInNAs based QWs have been the subject of extensive research, however their properties are far from ideal. Not only do the quantum dots exhibit a large size variation and thus a broad emission at 1.3μm but the threshold current density is highly temperature sensitive. As for GaInNAs it has been shown that even for the best devices available, approximately 50% of the threshold current at room temperature may be attributed to defect related recombination. An alternative is the use of GaAsSb/GaAs QWs. Lasers based upon this material have been successfully produced but remarkably little research has been undertaken to assess the carrier recombination and temperature dependent processes occurring in this material. This is perhaps all the more surprising given the wide uncertainly in the band alignment (type I versus type II) of the GaAsSb/GaAs interface for Sb~30-40% which will influence the device characteristics. The aim of this paper is to consider the characteristics of GaAsSb devices with the aim of learning more about their potential for use in 1.3μm VCSELs. In this study we investigated devices processes from wafers grown by Solid Source MBE. The QW region consists of 3, 7nm GaAs0.64Sb0.36 QWs with 5nm GaAs spacers and GaAsP barriers for strain compensation. The wafers were fabricated into broad area stripe lasers with stripe widths of 100μm and a cavity length of 1mm. The devices were measured as-cleaved. Temperature dependence measurements were performed with a standard closed cycle cryostat setup over the temperature range 60-300K. The integrated spontaneous emission (Lspon) versus current at two different temperatures, 110K and 260K, is shown in Fig. 1. At both temperatures, the integrated spontaneous emission pins at threshold due to the fact that the carrier density is prohibited from increasing by the lasing process. The two curves have been normalised to the value of Lspon at threshold, Lpin, so that the shape of both curves can be compared. At 110K, the Lspon versus current curve is linear suggesting that the primary current path flowing through the laser may be associated with radiative recombination. Furthermore, the fact that the curve remains linear down to the lowest currents suggests that defectrelated recombination is minimal and that the material quality is high. In stark contrast, the sublinear behaviour of the Lspon versus current curve at 260K suggests that a non-radiative process is present and that the process has a stronger dependence on the carrier density than the radiative current. 331 0-7803-9217-5/05/$20.00©2005 IEEE TuS4