Long-wavelength Vertical-cavity Surface-emitting Lasers Research Articles

Buried-heterostructure long-wavelength vertical-cavitysurface-emitting lasers with InGaAsP/InP-GaAs/AlAs DBRs

Thin-film wafer fusion has been used to fabricate 1.55 µm buried-heterostructure long-wavelength vertical-cavity surface-emitting lasers (LW-VCSELs) with InGaAsP/InP-GaAs/AlAs distributed Bragg reflectors. Room-temperature continuous-wave operation of the LW-VCSELs has been achieved with a threshold current of 2.1mA at 25°C.

Self-aligned current confinement structure using AlAs/InP tunnel junction in GaInAsP/InP semiconductor lasers

We propose a current confinement structure which can be self-formed by thermal annealing of a electrode metal with a self-aligning process. The migrated metal selectively destroys an AlAs/InP tunnel junction to form a high resistance isolation layer. The hole current can be injected through a preserved tunnel junction window. We confirmed its lateral confinement effect from the near-field pattern of fabricated GaInAsP/InP stripe lasers. The proposed current confinement structure is very simple and useful for the lateral injection in semiconductor optical devices including long-wavelength vertical-cavity surface-emitting lasers.

Room-temperature pulsed operation of GaAsSb/GaAsvertical-cavity surface-emitting lasers

GaAs-based long-wavelength vertical-cavity surface-emitting lasers with a GaAsSb quantum well active layer have been fabricated for the first time. Room temperature pulsed oscillation was obtained at a wavelength of 1.22 µm with a threshold current of 20 mA for devices with 25 µm square mesa.

AlAsSb-based distributed Bragg reflectorsusing InAlGaAs as high-index layer

The optical and electrical properties of InAlGaAs/AlAsSb distributed Bragg reflectors for long-wavelength vertical-cavity surface-emitting lasers are reported. This materials combination shows much lower resistances for p-type mirrors compared to AlGaAsSb/AlAsSb mirrors, resulting from a smaller valence band discontinuity.

Metamorphic DBR and tunnel-junction injection. A CW RT monolithic long-wavelength VCSEL

We present and give details about the conception and realization of the first monolithic long wavelength vertical-cavity surface-emitting laser (VCSEL) operating continuous wave at room temperature. This approach relies on two originalities: a metamorphic GaAs-AlAs distributed Bragg reflector and an injection through a reverse-biased tunnel junction. Record output powers as high as 1 mW and a maximum operating temperature of 47/spl deg/C have thus been achieved. Furthermore, in this paper, we present the optimization work on the different constituting parts of the VCSEL.

Superlattice AlAs/AlInAs-oxide current aperture for long wavelength InP-based vertical-cavity surface-emitting laser structure

A superlattice AlAs/AlInAs structure which can be formed on an InP substrate is proposed and demonstrated for use in oxide confinement long wavelength surface emitting lasers. The large strain of AlAs layers is relaxed by the use of a superlattice structure showing no defects and uniform oxidations. Also, an AlAs layer on an InP substrate provides us with a relatively large heterobarrier, and will be useful for improving temperature characteristics of long-wavelength vertical-cavity surface-emitting lasers. A current aperture of a few micrometers in diameter was formed by precisely controlling the oxidation time. We have demonstrated a current confinement by this oxide aperture. Low-threshold long-wavelength vertical-cavity surface-emitting lasers with this oxide confinement structure are expected.

Experimental method for high-accuracy reflectivity-spectrum measurements

An experimental method for accurate measurements of the reflectivity spectrum of mirrors is presented. It combines the noise reduction obtained with multiple beam reflections on two identical mirrors; high-beam quality, owing to the use of single-mode optical fibers; and high immunity against intensity variations of the beam. This method is demonstrated for characterizing a 30-period GaAs/Al(0.65)Ga(0.35)As distributed Bragg reflector designed for long-wavelength vertical-cavity surface-emitting lasers. Its peak reflectivity is found to be 99.43 ? 0.04% at 1.562 mum, and an optical absorption coefficient of alpha = 36 ? 6 cm(-1) is derived. The peak internal reflectivity of this distributed Bragg reflector used as the top mirror in a wafer-fused vertical-cavity surface-emitting laser is calculated to be 98.87 ? 0.12%, and the transmission is 0.28%.

Current spreading and carrier diffusion in long-wavelength vertical-cavity surface-emitting lasers

Current spreading and carrier diffusion in vertical cavity surface-emitting lasers (VCSELs) critically affect the threshold current density, transverse gain profile, and optical modal characteristics of the devices. We have numerically analyzed these effects for four popular long-wavelength VCSEL structures with wafer-bonded GaAs-AlGaAs Bragg bottom mirrors. The results show that current confinement for p-mirror VCSELs is approximately twice as effective as the corresponding n-mirror VCSEL's although the confinement factor for all practical VCSEL structures studied here is considerably lower than the ideal structure. Calculations also show a strong dependence of current confinement on device aperture size and a tradeoff between the optical modal property and the current confinement efficiency for different apertured devices.

InAsP/InGaAsP periodic gain structure for 1.5 μm vertical cavity surface emitting laser applications

We have studied the capabilities of chemical beam epitaxy (CBE) to produce high-gain media for long-wavelength (1.5 μm) vertical cavity surface emitting lasers (VCSELs). Using a parameter pair of low growth temperature and small V/III ratio the integration of up to 15 highly strained (1.78%) InAsP quantum wells (QWs) into a periodic gain structure (PGS) is successfully demonstrated. In this work we present data of atomic force microscopy (AFM), X-ray diffraction, reflectivity and electro-luminescence measurements that prove the very good structural and optical quality of this CBE grown PGS. As an alternative to conventional multi quantum well (MQW) systems as active layers, a high-performance PGS may be used in a VCSEL structure to reduce the very strict requirements on the InP-based distributed Bragg reflectors (DBRs) or to increase the achievable output power. Due to the use of thickness-reduced InP-based DBRs in conjunction with a PGS as the active region the fabrication of fully epitaxial grown long-wavelength VCSELs might also be possible with CBE.

Photopumped lasing at 1.25 μm of GaInNAs-GaAs multiple-quantum-well vertical-cavity surface-emitting lasers

We report room-temperature (RT) continuous-wave (CW) photopumped operation of long-wavelength vertical-cavity surface-emitting lasers (VCSELs) employing a Ga/sub 0.7/In/sub 0.3/N/sub 0.007/As/sub 0.993/-GaAs multiple-quantum-well (MQW) active layer grown directly on a GaAs-AlAs distributed Bragg reflector (DBR). Evidence for laser oscillation includes spectral linewidth narrowing, clamping of spontaneous emission, and a distinct increase in slope efficiency at threshold. By taking advantage of lateral growth rate nonuniformity, we obtained laser emission over an extremely broad 110-nm wavelength range, from 1.146-1.256 μm. Equivalent threshold current density over this range was estimated at 3.3-10 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

The effective frequency method in the analysis of vertical-cavity surface-emitting lasers

An effective index model for vertical-cavity surface-emitting lasers (VCSELs) is reexamined. In a systematic manner, the basic equations are derived. Instead of effective indices of plane reference waveguides, effective frequencies of plane reference resonators appear. Calculations of the threshold gain and lasing wavelength of a long-wavelength VCSEL show the usefulness of the method and clarify the waveguiding mechanisms in VCSELs, Both dispersion and waveguiding influence the lasing wavelength remarkably.

Simulation and analysis of 1.55 μm double-fused vertical-cavity lasers

Using a comprehensive numerical model, we analyze the first long-wavelength (1.55 μm) vertical-cavity surface-emitting lasers operating continuous-wave at room temperature (up to 33 °C). These double-fused lasers employ strain-compensated InGaAsP multi-quantum wells sandwiched between GaAs/AlGaAs distributed Bragg reflectors that are fused on both sides of the InP spacer. The two-dimensional model includes drift and diffusion of electrons and holes, finite-element thermal analysis, calculation of the internal optical field at threshold, and k⋅p band structure computations. The simulation shows excellent agreement with a large variety of experimental characteristics. Internal laser parameters like optical losses and injection efficiency are obtained. The thermal conductivity of the multilayer mirror is found to be only one third of the value expected. Temperature dependent absorption and Auger recombination within the active region as well as lateral leakage currents are identified as dominating loss mechanisms. The analysis shows great potential for high-temperature operation of double-fused vertical-cavity lasers.

Numerical modeling of undercut ridge VCSELs designed for CW operation at 1.3 μm: design optimization

Optimized undercut ridge long-wavelength vertical-cavity surface-emitting semiconductor lasers (LW-VCSEL's) are investigated and the influence of thermal effects on the light versus current characteristics is analyzed by thermal-electric, optical, and electronic modeling. The model includes nonuniform current injection, carrier diffusion, stimulated emission, distributed heat sources, and active material band structure calculations. Device parameters such as thermal resistance, threshold current, and external quantum efficiency are evaluated, in an attempt to provide an understanding of the current-funneling mechanism and the thermal limitations of such devices. Simulated power versus current characteristics exhibit the typical thermal roll-over in CW operation.

Long-Wavelength Vertical-Cavity Surface-Emitting Laser Diodes

AbstractLong-wavelength (1300/1550 nm) vertical-cavity surface-emitting lasers (VCSELs) have been much more difficult to realize than VCSELs at shorter wavelengths such as 850/980 nm. The primary reason for this has been the low refractive index difference and reflectivity associated with lattice-matched InP/InGaAsP mirrors. A solution to this problem is to “wafer-fuse” high-reflectivity GaAs/AlGaAs mirrors to InP/InGaAsP active regions. This process has led to the first room-temperature continuous-wave (CW) 1.54 μm VCSELs. In this paper, we discuss two device geometries which employ wafer-fused mirrors, both of which lead to CW operation. We also discuss fabrication of WDM arrays using long-wavelength VCSELs.

Effective thermal conductivity analysis of 1.55 μm InGaAsP/InP vertical-cavity top-surface-emitting microlasers

An analytical approach is developed and appoied to investigate the thermal properties of 1.55 μm microresonator vertical-cavity surface-emitting lasers (VCSELs) mounted substrate-down. The results indicate that difficulties with obtaining the CW operation of long-wavelength VCSELs are primarily associated with intrinsic properties (such as low T0) rather than with their thermal resistance.