Oxide‐free vertical‐cavity surface‐emitting lasers with low junction temperature and high drive level

Abstract

Data are presented showing that lithographic vertical-cavity surfaceemitting lasers (VCSELs) produce minimal junction temperature rise compared to oxide VCSELs. Eliminating the thermal block caused by internal oxides combined with improved mirror materials reduces the junction temperature. The elimination of internal oxide, lower junction temperature and reduced internal strain promise increased reliability in the new VCSELs. Power conversion efficiencies in excess of ∼50% are reported, even for very small lithographic VCSELs.Introduction: When a laser diode is electrically biased, its junction temperature rises above the temperature of its thermal mount. This junction temperature influences many of the key laser diode parameters, including reliability, modulation speed and efficiency. Vertical-cavity surface-emitting lasers' (VCSEL) reliability, especially, has been shown to track junction temperature rise during operation over a wide range of operating conditions [1][2][3][4][5][6]. The VCSEL reliability is limited by defect propagation, usually from the oxide aperture, and wear-out. When the junction temperature is elevated relative to the thermal mount as a result of electrical biasing, internal strain fields are increased around the oxide aperture termination and lead to defect propagation from the aperture [2]. Exposure of the oxide VCSEL to moisture can dramatically accelerate this defect propagation [4].In this Letter, we show that lithographic VCSELs not only eliminate the oxide reliability problems, but also will operate at a low junction temperature. The low junction temperature can extend wear-out lifetime and reduce the internal intrinsic device strain that results from electrical biasing. This combination appears to be capable of realising highly reliable VCSELs which are much more reliable than oxide VCSELs today. The data also indicate that smaller VCSELs can produce higher reliability than larger VCSELs. This is because smaller VCSELs can operate at lower junction temperatures at similar, or even higher, current densities.The data that is presented is measured for lithographic VCSELs, with varying sizes from a single wafer. The low junction temperature in the lithographic VCSELs results from eliminating the thermal barrier caused by the oxide, by incorporating high thermal conductivity AlAs as the low index mirror material in both the n-type and p-type mirror layers, and by using a high-efficiency design.

Small-sized lithographic single-mode VCSELs with high-power conversion efficiency

“…We have shown 8xx-nm lithographic VCSELs have approximately a factor of two lower thermal resistance than in oxide VCSELs [5]. We have also shown 3 µm lithographic VCSELs have approximately a factor of two lower junction temperature rise than 3 µm oxide VCSEL under the same bias current density of 50 kA/cm 2 , and lithographic VCSELs can be driven at a much higher current density before thermal rollover [6]. These are the evidence that lithographic VCSELs can have higher reliability than the oxide.…”

AlGaAs Tunnel Junction (TJ)-VCSELs: A NEGF–Drift-Diffusion Approach

“…An even more interesting design could involve the photolithographic definition of buried TJs, to get rid of the wet oxidation process that limits the effectiveness of confinement when going to small oxide diameters [63], [64]. At the same time, the definition of a mesa would not be necessary any more, resulting in denser VCSEL arrays [65], [66].…”

901 nm Lithographic vertical‐cavity surface‐emitting laser with stable single‐lobed beam pattern

“…Experiment results: The lithographic VCSELs are using an epitaxial confinement region described previously [1][2][3]. Various sizes are fabricated with test results presented for 6 and 2 µm diameters.…”