Effect of Al−content reduction in (AlGa)As cladding layers of MOVPE grown high−power laser diodes (original) (raw)
Related papers
2004
We studied symmetric and asymmetric InGaAsP-In-GaAs 1.55-m multiquantum-well (MQW) laser diodes (LDs) with highly p-doped layers in the two-step separate confinement heterostructure (SCH). The p-doping in p-SCH suppresses the electron overflow from the MQWs to p-SCH, but it is an origin of free carrier absorption loss. An additional InGaAsP layer inserted inside n-SCH makes asymmetric field distribution and, therefore, reduces the portion of optical field distribution in highly p-doped regions with high optical loss. Compared with symmetric structure, asymmetric SCH LD has low threshold current density, low internal loss, and high and flat slope efficiency with respect to temperature. Index Terms-Asymmetric separate confinement heterostructure (SCH), high p-doping, light-current (-) rollover. I. INTRODUCTION I N COMPARISON with AlGaAs-GaAs system, In-GaAsP-InP systems are still suffering from the low conduction band offset and, thus, the injected carriers easily overflow from multiquantum-well (MQW) active layer into the separate confinement heterostructure (SCH) layer. This phenomenon is responsible for power saturation [1], the decrease of the differential quantum efficiency [2], and instability at higher temperature and/or higher power operation of the MQW laser diodes (LDs) [3]. Recently, high p-doping at the interface between first and second SCH layers and/or in the p-SCH layer have been utilized to suppress the electron overflow [1], [4]. However, it seems that the effect of high p-doping, that is, the suppression of electron leakage, is obtained at the expense of optical gain. As one of the solutions to reduce optical loss (free carrier absorption) in highly doped cladding layers, Garbuzov et al. proposed broadened waveguides instead of strong index waveguides and improved the light-current (-) performance [8], [9]. Meanwhile, it is well known that the absorption coefficient in the p-doped material is higher than that in the n-doped material even in the same doping concentrations [5], [6].
Study on InGaAsP–InGaAs MQW-LD With Symmetric and Asymmetric Separate Confinement Heterostructure
IEEE Photonics Technology Letters, 2004
We studied symmetric and asymmetric InGaAsP-In-GaAs 1.55-m multiquantum-well (MQW) laser diodes (LDs) with highly p-doped layers in the two-step separate confinement heterostructure (SCH). The p-doping in p-SCH suppresses the electron overflow from the MQWs to p-SCH, but it is an origin of free carrier absorption loss. An additional InGaAsP layer inserted inside n-SCH makes asymmetric field distribution and, therefore, reduces the portion of optical field distribution in highly p-doped regions with high optical loss. Compared with symmetric structure, asymmetric SCH LD has low threshold current density, low internal loss, and high and flat slope efficiency with respect to temperature. Index Terms-Asymmetric separate confinement heterostructure (SCH), high p-doping, light-current (-) rollover. I. INTRODUCTION I N COMPARISON with AlGaAs-GaAs system, In-GaAsP-InP systems are still suffering from the low conduction band offset and, thus, the injected carriers easily overflow from multiquantum-well (MQW) active layer into the separate confinement heterostructure (SCH) layer. This phenomenon is responsible for power saturation [1], the decrease of the differential quantum efficiency [2], and instability at higher temperature and/or higher power operation of the MQW laser diodes (LDs) [3]. Recently, high p-doping at the interface between first and second SCH layers and/or in the p-SCH layer have been utilized to suppress the electron overflow [1], [4]. However, it seems that the effect of high p-doping, that is, the suppression of electron leakage, is obtained at the expense of optical gain. As one of the solutions to reduce optical loss (free carrier absorption) in highly doped cladding layers, Garbuzov et al. proposed broadened waveguides instead of strong index waveguides and improved the light-current (-) performance [8], [9]. Meanwhile, it is well known that the absorption coefficient in the p-doped material is higher than that in the n-doped material even in the same doping concentrations [5], [6].
Optimization of GaAsP-QWs for high-power diode lasers at 800 nm
In-Plane Semiconductor Lasers IV, 2000
Tensile-strained GaAsP quantum wells (QWs) embedded in AJGaAs waveguide and cladding layers are an alternative approach for the wavelength range 700-800 nm. We will present a detailed experimental and theoretical study of the dependence of the threshold current on the thickness and the strain of the QW for 800 nm. The optimum thickness of the GaAsP QW for a minimum threshold current density is about 14 nm and is thus much larger than for compressively strained QWs. Higher characteristic temperatures T0 can be obtained with even thicker QWs. In order to achieve high optical output powers and good fiber coupling efficiencies, we used broad waveguides with weak optical confinement and small far field divergence. We prepared two structures with 1 tm thick A1065Ga35As (structure A) and 2 tm thick Al045Ga55As (structure B) waveguides, respectively. For structure B, the thickness of the Al070Ga30As cladding layers must be carefully optimized in order to suppress higher-order transverse modes. Whereas structure B yields a higher maximum cw output power of AR/HR coated broad-area devices, structure A shows a better high-temperature behavior. Aging tests performed at 2 W (100 j.m stripe width) and 25°C suggest a very good reliability of these devices.
MOVPE growth of AlGaAs/GaInP diode lasers
Journal of Electronic …, 2000
High power diode lasers operating in the wavelength range 730-1060 nm are of significant interest for applications like pumping fiber amplifiers and solid-state lasers, for soldering, material processing or for applications in medicine, spectroscopy and metrology. In recent years Al-free diode lasers have shown improved performance in terms of output power 1 and long-term reliability. 2 Further, the fabrication of buried laser structures is facilitated in the absence of Al. However, the growth of GaInP and InGaAsP alloys on GaAs turns out to be challenging due to difficulties in growing thick ternary and quaternary layers that are precisely lattice-matched and due to miscibility and ordering problems. 3-5 These result in composition fluctuations and rough surfaces. To overcome these problems but to keep most of the advantages of the Al-free system we have combined GaInP waveguide layers with AlGaAs cladding layers for different types of diode laser structures. The formation of abrupt heterointerfaces between AlGaAs and InGaP is crucial for high power devices with good reliability. Several studies have characterized the GaInP/GaAs interface 6,7 and a quaternary intermediate layer between GaInP and GaAs has been re
Optimization of GaAsP-QWs for high-power diode lasers at 800 nm
Storage and Retrieval for Image and Video Databases, 2000
Tensile-strained GaAsP quantum wells (QWs) embedded in AlGaAs waveguide and cladding layers are an alternative approach for the wavelength range 700 - 800 nm. We will present a detailed experimental and theoretical study of the dependence of the threshold current on the thickness and the strain of the QW for 800 nm. The optimum thickness of the GaAsP QW for
We fabricated both symmetric and asymmetric InGaAsP/InGaAs 1.55 µm MQW-LD's with highly p-doped layers in the two-step SCH. The asymmetric structure has additional 100 nm InGaAsP layer in n-type SCH region. The symmetric and asymmetric SCH LD's show threshold current densities of 1.3 kA/cm 2 and 0.7 kA/cm 2 , and differential slope efficiencies of 0.11 W/A and 0.10 W/A. respectively. Internal loss of the asymmetric structure was measured to be 12.7 cm-1 , whereas that of symmetric structure was 20 cm-1. The reduction of internal loss in asymmetric structure indicates that the portion of the optical mode in the highly doped region is effectively reduced (calculation showed reduction from 47% to 40%). The internal quantum efficiency and the characteristic temperature also improved in asymmetric structure.
Optics Express, 2011
The effect of polarization-matched Al 0.25 In 0.08 Ga 0.67 N electronblocking layer (EBL) on the optical performance of ultraviolet Al 0.08 In 0.08 Ga 0.84 N/ Al 0.1 In 0.01 Ga 0.84 N multi-quantum well (MQW) laser diodes (LDs) was investigated. The polarization-matched Al 0.25 In 0.08 Ga 0.67 N electron blocking layer (EBL) was employed in an attempt to reduce the polarization effect inside the active region of the diodes. The device performance which is affected by piezoelectric was studied via driftdiffusion model for carrier transport, optical gain and losses using the simulation program of Integrated System Engineering Technical Computer Aided design (ISE TCAD). The optical performance of the LD using quaternary Al 0.25 In 0.08 Ga 0.67 N EBL was compared with the LD using ternary Al 0.3 Ga 0.7 N EBL where both materials have the same energy band gap of E g = 3.53 eV. The self-consistent ISE-TCAD simulation program results showed that the polarization-matched quaternary Al 0.25 In 0.08 Ga 0.67 N EBL is beneficial as it confines the electrons inside the quantum well region better than ternary Al 0.3 Ga 0.7 N EBL. The results indicated that the use of Al 0.25 In 0.08 Ga 0.67 N EBL has lower threshold current and higher optical intensity than those for Al 0.3 Ga 0.7 N EBL. The effect of Al 0.25 In 0.08 Ga 0.67 N EBL thickness on the performance of LDs has also been studied. Results at room temperature indicated that lower threshold current, high slope efficiency, high output power, and high differential quantum efficiency DQE occurred when the thickness of Al 0.25 In 0.08 Ga 0.67 N EBL was 0.25 µm.