Overgrown GaN Substrates Research Articles

Super High Power Blue-violet Semiconductor Laser Array

This paper describes the development of super-high-power (SHP) AlGaInN-based blue-violet laser diode (LD) arrays. In 2001, the LD arrays were successfully fabricated using epitaxially laterally overgrown GaN substrates. The LD array consisted of 11 laser chips, each with 4 stripe emitters monolithically integrated. A maximum light output power of 4.2 W under continuous-wave (cw) operation at 25°C was achieved for the first time, demonstrating the highly uniform quality of the fabricated laser chips. In 2003, we reported a new SHP blue-violet LD composed of a single broad-area stripe emitter on a GaN substrate. A maximum light output power of 0.94 W under cw operation at 20 °C was achieved for the sample with the stripe width of 10 μm. An array of 11 of these LDs was also successfully fabricated, producing a combined light output power of over 6.1 W under cw operation at 20 °C.

Glide along non‐basal slip planes in InGaN epilayers

We have observed a systematic nucleation of misfit dislocations at the InGaN/GaN heterointerface. This occurs when InGaN films are grown on an epitaxially laterally overgrown GaN substrate with a reduced dislocation density. The misfit dislocations are aligned along 〈〉 directions forming a symmetric hexagonal array. Potential wurtzite slip systems were analysed by extending the Matthews-Blakeslee model to include Peierls forces. Due to an inactive basal plane in the c-growth direction, non-basal slip is necessary for plastic relaxation. The active slip system was identified to be {} 〈〉. The possibility of activation of other slip systems is also discussed. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of GaN-based Laser Diodes in Near Ultraviolet Region

Ultraviolet (UV) laser diodes (LDs) were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. We fabricated three types of UV LDs whose active layers were (I) ternary InGaN, (II) quaternary AlInGaN and (III) binary GaN single quantum well (SQW) structures. We investigated the LD characteristics in detail in the near UV region. LDs whose active layers were quaternary Al0.03In0.02Ga0.95N were demonstrated under the pulsed-current-biased conditions at room temperature. The emission wavelength of these LDs was the shortest wavelength (366.4 nm) in our experiments. We also demonstrated binary GaN SQW LDs for the first time. The threshold current density, voltage and emission wavelength of these LDs under 25°C continuous-wave (cw) operation were 3.5 kA/cm2, 4.6 V and 369.0 nm, respectively. The estimated lifetime was approximately 2000 h under 25°C cw operation at an output power of 2 mW.

Performance and degradation of continuous-wave InGaN multiple-quantum-well laser diodes on epitaxially laterally overgrown GaN substrates

The performance and degradation characteristics of continuous-wave (cw) InGaN multiple-quantum-well laser diodes are reported. A cw threshold current as low as 62 mA was obtained for ridge-waveguide laser diodes on epitaxially laterally overgrown GaN on sapphire substrates grown by metalorganic chemical vapor deposition. Transmission electron microscopy reveals a defect density <5×107 cm−2 in the active region. The emission wavelength was near 400 nm with output powers greater than 20 mW per facet. Under cw conditions, laser oscillation was observed up to 70 °C. The room-temperature cw operation lifetimes, measured at a constant output power of 2 mW, exceeded 15 h. From the temperature dependence of the laser diode lifetimes, an activation energy of 0.50 eV±0.05 eV was determined.

Blue InGaN-based laser diodes with an emission wavelength of 450 nm

Blue InGaN single-quantum-well-structure laser diodes (LDs) with an emission wavelength of 450 nm were grown on an epitaxially laterally overgrown GaN substrate by a metalorganic chemical vapor deposition method. The threshold current density and voltage were 4.6 kA cm−2 and 6.1 V, respectively. The estimated lifetime was approximately 200 h under room-temperature continuous-wave operation at an output power of 5 mW. When the number of InGaN well layers of the LDs with emission wavelengths longer than 435 nm varied from one to three, the lowest threshold current density was obtained when the number of well layers was one.

InGaN/GaN/AlGaN-based laser diodes with modulation-doped strained-layer superlattices grown on an epitaxially laterally overgrown GaN substrate

InGaN multi-quantum-well-structure laser diodes with Al0.14Ga0.86N/GaN modulation doped strained-layer superlattice cladding layers grown on an epitaxially laterally overgrown GaN (ELOG) substrate was demonstrated to have a lifetime of more than 1150 h under room-temperature continuous-wave operation. After 4 μm etching of the ELOG substrate, the etch pit density was about 2×108 cm2 in the region of the 4-μm-wide stripe window, but almost zero in the region of the 7-μm-wide SiO2 stripe.

InGaN multiquantum-well-structure laser diodes with GaN-AlGaN modulation-doped strained-layer superlattices

InGaN multiquantum-well-structure (MQW) laser diodes with Al/sub 0.14/Ga/sub 0.86/N-GaN modulation doped strained-layer superlattice (MD-SLS) cladding layers grown on an epitaxially laterally overgrown GaN substrate was demonstrated to have a lifetime of more than 2300 h under the condition of room-temperature continuous-wave operation. The self-pulsation was observed with a frequency of 3.5 GHz. The relative intensity noise less than -145 dB/Hz was obtained even at the 6% optical feedback using the high-frequency modulation of 600 MHz. The threshold carrier density of the InGaN MQW-structure laser diodes was estimated to be 3/spl times/10/sup 19//cm/sup 3/ using a carrier lifetime of 1.8 ns.

InGaN/GaN/AiGaN-Based Laser Diodes with an Estimated Lifetime of Longer than 10,000 Hours

AbstractInGaN multi-quantum-well (MQW) structure laser diodes with A10.14Ga0.86N/GaN modulation doped strained-layer superlattice cladding layers grown on an epitaxially laterally overgrown GaN substrate were demonstrated to have an estimated lifetime of more than 10,000 hours under continuous-wave operation at 20°C. Under operation at a high temperature of 50°C, the lifetime was longer than 1,000 hours. The activation energy of the lifetime was estimated to be 0.5 eV. With the operating current increasing above the threshold, a self-pulsation with a high frequency of 3.5 GHz was observed. The relative intensity noise (RIN) less than -145 dB/Hz was obtained even at the 6% optical feedback using the high-frequency modulation of 600 MHz. The threshold carrier density of the InGaN MQW-structure LDs was estimated to be 3 × 1019/cm3 using a carrier lifetime of 1.8 ns.