High-efficiency green laser diodes remain a challenge for researchers and manufacturers due to several factors intrinsic to the InAlGaN material system. Notably, the high indium content quantum wells (QW) are sensitive to thermal damage in the form of indium segregation, particularly when the QWs are exposed to the high-temperature growth steps of the ptype AlGaN cladding layers in MOCVD. This paper presents device results from blue distributed feedback (DFB) laser diodes grown entirely by MOCVD compared to material grown by MOCVD through the active region and overgrown with low-temperature p-AlGaN using remote plasma chemical vapor deposition (RPCVD). Preliminary data demonstrate comparable performance from MOCVD-only and MOCVD with RPCVD p-cladding, showing a full-width at half maximum emission of 3 pm and side mode suppression ratio of 19 dB. RPCVD enables the growth of high-quality ptype AlGaN layers at temperatures below the thermal damage threshold of In-rich QWs, leading to longer wavelength devices. The degree of thermal damage to the In-rich green QWs is assessed using fluorescence microscopy to directly compare the RPCVD-enhanced p-AlGaN growths at various growth temperatures over all-MOCVD n-side and green quantum wells.
InAlGaN-based laser diodes (LDs) can be designed to emit across a wide range of wavelengths spanning UV to green. A common challenge across all wavelengths lies in the difficulty in producing low resistance p-type InAlGaN layers. For shorter wavelength devices, the requirement of high aluminium containing p-AlGaN leads to high device series resistance. For the longer wavelength devices approaching the green wavelengths, the thermal degradation of the indium-rich quantum wells during the growth of the p-GaN and p-AlGaN cladding layers reduces the device efficiency. In this paper we discuss how BluGlass’s remote plasma chemical vapour deposition (RPCVD) technology can address these challenges through improvements to intrinsic material properties as well as enabling novel design architectures.
The unique growth conditions of BluGlass’ low growth temperature technology Remote Plasma Chemical Vapour Deposition (RPCVD) are capable of producing Activate As-Grown (AAG) buried p-GaN layers. This ability renders RPCVD a highly attractive technique to produce GaN-based Tunnel Junctions (TJ) without the complexities associated with the post-growth lateral activation steps required by MOCVD. In this paper we discuss the use of hybrid RPCVD/MOCVD TJs for MOCVD-grown ridge guide laser diode (LD) applications. The impact of both the structure and placement of the TJ on the total optical loss of the LD are investigated. TJs conforming to the strict compositional requirements in order to yield a net reduction in optical loss are demonstrated, paving the way to improved conversion efficiencies through the replacement of the highly resistive p-AlGaN cladding layers and p-type Ohmic contacts with lower resistance n-AlGaN cladding layers and n-type Ohmic contacts.
KEYWORDS: Semiconductor lasers, Cladding, Near field optics, Waveguides, Laser damage threshold, Structural design, Absorption, Reliability, Free space optics, Near field
We present a single-mode, 808 nm, AlInGaAs/AlGaAs/GaAs, strained, quantum-well laser with a record low, vertical divergence-angle of 12 degrees and high slope-efficiency of 1.0 W/A. Epitaxial-up mounted
devices have operated with no measurable degradation at 150 mW, 50°C for 3500 hours.
KEYWORDS: Quantum wells, Waveguides, Near field optics, Doping, Cladding, High power lasers, Metalorganic chemical vapor deposition, Semiconductor lasers, Absorption, Carbon
We report results on single-mode, InAlGaAs/AlGaAs/GaAs, 915 nm, lser-diodes operating reliably at 300 mW. The graded-index, separate-confinement, strained, single quantum-well structure was grown by metal-organic chemical-vapor deposition. Carbon, rather than zinc, was used as the p-doping srouce to reduce internal loss and potential reliability issues due to the thermal diffusion of zinc. A threshold current density of 133 A/cm2, internal loss of 2.0 cm-1 and internal quatnum efficiency of 93% were achieved. FOr 1500 μm long ridge waveguide lasers, a record single-mode output-power of 500mW was obtained for devices mounted epitaxial-side up onto AlN submounts using eutectic Au80Sn20 solder. Ten burned-in devices have now been aged at a constant current of 450 mA at 85°C for more than 1500 hours wihtout measurable degradation.
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