Realization of GaN-based gain-guided blue laser diodes by helium ion implantation
Qi ZhangShuming ZhangFeng ZhangJunjie HuMeixin FengMasao IkedaDeyao LiJianping LiuWeiguang YangLiqun ZhangHui Yang
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Abstract:
The fabrication process and characteristics of gallium nitride (GaN) based gain-guided blue laser diodes (LDs) are studied, in which an ion implantation process is adopted to confine carrier injection into the active region. The implantation of helium ions with an energy of 85 keV, an angle of 0°, and a dosage of 4.7 × 1014 cm−2 is conducted in the experiment. The specific contact resistivity of p-type ohmic contact of implanted sample is determined to be 2.2 × 10–4 Ω cm2, which is comparable with the un-implanted sample. Then, both ion-implanted gain-guided and ridge waveguide LDs are fabricated at the same time. Similar threshold current density and slope efficiency are obtained, while the operation voltage of ion-implanted gain-guided LDs is 0.2 V lower than the ridge waveguide LDs at 0.56 kA cm−2. The ridge waveguide LDs show multi-mode operation after lasing. However, for ion-implanted gain-guided LDs, the far-field pattern indicates a single lateral mode operation up to twice of the threshold current, and the peak optical output power of blue single mode LDs at 450 nm exceeds 200 mW under pulsed condition.Keywords:
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High-power GaInP/GaAlInP visible laser diodes operating at 630-nm band wavelength are promising as a replacement of He-Ne lasers for various uses such as optical recording, bar code readers, and laser printers. However, high threshold current densities (Jth) and low differential quantum efficiencies (ηd) have limited this utilization. Recently, low Jth. values ot 1.2 kA/cm3 (637 nm) and 1.7 kA/cm2 (635 nm) laser diodes made with strained MQW laser diodes were reported, but the output powers were modest (150 mW at 637 nm and 610 mW at 635 nm).1,2. Since the threshold current of SQW laser diodes is lower than that of MQWs and the Jth of SQWs decreases as the cavity length increases, the SQW structure is a good candidate for lowering the Jth. Moreover, since the ηd·of QW structures is strongly dependent on the optical cavity length, by carefully selecting the cavity length and the facet reflectivity, the device performance can be improved.
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The development of near ultraviolet laser diodes based on the AlGaN materials system on single crystal GaN substrates is presented. This includes growth of relaxed Ga-rich AlGaN layers, design of UV laser diodes, as well as discussion of the electrical and optical properties. We show that with the demonstration of optically pumped lasers, a pathway toward electrically injected laser diodes is available.
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Tensile-strained active layer GaAs/AlGaAs separateconfinement- heterostructure quantum-well lasers are reported. These lasers oscillate in the 780 nm band in the TM mode by TM mode gain enhancement in the tensile-strained active layer. The threshold current density of single-quantum-well laser diodes increases rapidly with heatsink temperature. However, triple-quantum-well laser diodes with a cavity length of 485–110 μm oscillated with a threshold current density 1–4 and 30 kA/cm2.
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The utilization of visible laser diodes for laser printing is discussed. First, the characteristics of a multiple- element array of single-mode, individually-addressed red (AlGaInP) laser diodes is described. The benefit of shorter- wavelength blue lasers is then evaluated. Finally, towards the realization of a blue laser diode, we describe results for AlGaInN and its heterostructures, which have been grown by OMVPE and characterized, including electrical injection and optical pumping of InGaN/AlGaN heterostructures.
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In this paper we present a detailed analysis of the degradation of InGaN-based laser diodes carried out by means of electrical and optical techniques. The study is based on the comparison between the degradation kinetics of laser diodes and light-emitting diode (LED)-like samples, i.e., devices with the same epitaxial structure as the lasers, but with no ridge and facets. Results described in the following indicate that degradation of lasers and LED-like samples is due to the same mechanism, possibly involving the generation of point defects within the active region of the devices. Furthermore, since degradation occurs both in lasers and in LED-like samples (i.e., structures with no current confinement), results suggest that degradation of lasers is not correlated with the geometry of the devices, nor to worsening of current confinement under the ridge.
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The authors review recent progress in the development of new materials for III-V semiconductor diode lasers useful for pumping solid-state lasers. All of the diode lasers discussed are grown on GaAs substrates. Particular emphasis is placed on the performance and reliability of high-CW-power strained-layer InGaAs-AlGaAs diode lasers emitting in the wavelength range between 0.87 and 1.1 mu m, improved resistance to degradation of 0.78 to 0.87 mu m diode lasers afforded by the strained-layer AlInGaAs-AlGaAs and lattice-matched GaInAsP-GaInP materials systems, and improved performance of visible diode lasers utilizing the materials system GaInP-AlGaInP.< >
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Proton radiation damage in laser diodes is investigated for several types of laser diodes with wavelengths from 650 to 1550 nm. Key parameters include slope efficiency, threshold current, and the transition characteristics between laser-emitting diode (LED) and laser operation. Some of the devices exhibited nonlinear relationships between threshold current and proton fluence. All of the lasers, including vertical-cavity surface-emitting lasers, were strongly affected by recombination-enhanced annealing, in contrast to double-heterojunction LEDs, which are only slightly affected by annealing. Analysis of laser characteristics after irradiation showed that the main effect of radiation damage is an increase in bulk recombination that increases loss within the laser cavity.
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In this paper we report on progress in the development of nitride laser diodes by molecular beam epitaxy (MBE). We review the steps taken to achieve continuous wave (CW) operation of 405nm lasers grown by MBE and evaluate the performance of such devices. The future potential of the growth method for lasers depends on the demonstration of long lived lasers with good operating characteristics such as high power output and low threshold current. We assess the challenges to achieving such performance in MBE-grown lasers and the progress in evaluating the key laser parameters in our devices.
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