Uncoated Facets Research Articles

Submilliampere threshold buried-heterostructure InGaAs/GaAs single quantum well lasers grown by selective-area epitaxy

Strained-layer InGaAs-GaAs-AlGaAs single quantum well buried heterostructure lasers grown by selective-area MOCVD are described. Threshold currents of 2.65 mA for an uncoated device and 0.97 mA for a coated device have been obtained. A peak optical output power of 170 mW per uncoated facet for a device with a 4 /spl mu/m active region width was also achieved. Peak emissions wavelengths range from 0.956 to 1.032 /spl mu/m. >

High-power InGaAsP/GaAs 0.8-μm laser diodes and peculiarities of operational characteristics

High-power operation of 3 W in pulse mode, 750 mW in quasi-continuous wave and 650 mW in continuous wave per uncoated facet from 100-μm aperture has been demonstrated for 1-mm-long cavity InGaAsP/GaAs 808-nm laser diodes prepared by low-pressure metalorganic chemical vapor deposition. Threshold current density of 300 A/cm2, differential efficiency of 1.1 W/A, T0=155 °C, transverse beam divergence of 27°, and less than 2-nm linewidth at 808 nm have been measured. No degradation has been observed after 1000 h of operation in a quasi-continuous wave regime.

Buried-oxide ridge-waveguide InAlAs-InP-InGaAsP (λ∼1.3 μm) quantum well heterostructure laser diodes

Native oxide technology is used to fabricate long wavelength (λ∼1.3 μm) InAlAs-InP-InGaAsP quantum well heterostructure laser diodes with a buried oxide undercutting and constricting the ridge-waveguide active region. The buried native oxide of InAlAs constricts the current and reduces edge and surface losses. Data are presented showing threshold currents as low as ∼140 mA for ∼13-μm-wide stripes (L∼750 μm), with maximum continuous wave output powers as high as ∼225 mW/facet and external differential quantum efficiencies up to 67% (300 K, uncoated facets).

High temperature operation of 1.3 μm ridge waveguide lasers using lattice matched and strained multiple quantum wells

We report the high temperature operation of 1.3 μm ridge waveguide Fabry–Perot lasers utilizing a double-carrier-confinement heterostructure, with an active region containing an n-type lattice-matched multiple quantum well (MQW) as well as a p-type strained MQW. All devices with a cavity length of 400–1000 μm and as-cleaved uncoated facets operated beyond 100 °C in the cw mode with an optical power in excess of 8 mW. T0 was found to be in the range of 65–75 and 72–98 K, for uncoated devices and devices with one high-reflectivity-coated facet, respectively.

Long wavelength (λ∼1.5 μm) native-oxide-defined InAlAs-InP-InGaAsP quantum well heterostructure laser diodes

Native oxidation (‘‘wet’’ oxidation via H2O vapor+N2) of InAlAs is employed to fabricate long wavelength (λ∼1.5 μm) InAlAs-InP-InGaAsP quantum well heterostructure laser diodes. Data are presented on gain-guided native-oxide-defined stripe-geometry lasers (40 μm×500 μm) with threshold currents of 200 mA (1 kA/cm2) emitting with multiple longitudinal modes centered at λ∼1.5 μm. The threshold currents, approximated as Ith=I0 exp(T/T0), exhibit a characteristic temperature of T0∼49 K and an operating temperature as high as T=70 °C. Maximum continuous output powers of 140 mW/facet (uncoated facets) and a differential quantum efficiency of 38% are achieved.

Planar single-facet teardrop-shaped AlxGa1−xAs-GaAs quantum well heterostructure laser

Data are presented demonstrating the laser operation of an AlxGa1−xAs-GaAs quantum well heterostructure (QWH) crystal patterned into a smoothly curved folded resonator, a ‘‘teardrop’’-shaped resonator, with a single output facet. A deep AlxGa1−xAs native oxide formed entirely through the top confining layer is utilized to produce a large effective index step for lateral optical confinement. The teardrop-shaped laser operates primarily in a TM (transverse magnetic) longitudinal mode polarized with a TM/TE (transverse electric) power ratio of 7:1. Continuous wave 300 K threshold currents as low as ∼127 mA, external differential quantum efficiencies of η∼15%, and total output power in excess of 75 mW (uncoated facet) are achieved.

Blue/green laser diodes and light emitting diodes

We report the properties of blue/green laser diodes and light emitting diodes based on ZnSe-related II–VI semiconductor heterostructures. For blue/green laser diodes, threshold voltages for stimulated emission as low as 12 V at 77 K have been achieved using HgSe ohmic contacts. Differential quantum efficiencies as large as 36% per (uncoated) facet has been obtained for some of the laser diodes. Stimulated emission at wavelengths as short as 467.5 nm has been observed at 77 K. In addition, blue/green LED encapsulated lamps have been fabricated and tested. Power efficiencies as large as 7×10 -4 have been obtained at 300 K for green LEDS which employ ZnSTeSe quantum wells. These devices exhibit power efficiencies greater than one percent (>10 -2) in the temperature range 120–200 K.

Calculated room-temperature threshold current densities for the visible II-VI ZnCdSe/ZnSe quantum-well diode lasers

Room-temperature threshold current densities for the visible II-VI ZnCdSe/ZnSe semiconductor quantum-well diode lasers have been calculated using a simple model for the quantum-well gain and spontaneous radiative recombination rate. These results are compared with those for the infrared III-V GaAs/GaAlAs quantum-well lasers, calculated using the same model. By tailoring the epitaxial structure for optimum optical confinement, cw room-temperature operation of the ZnCdSe/ZnSe quantum-well lasers should be possible with threshold current densities as low as 400 A/cm2 for a 1-mm cavity length and uncoated laser facets, assuming the problem of ohmic contacts to the epitaxial structure is resolved.

InGaAs/GaAs strained quantum wire lasers grown by organometallic chemical vapor deposition on nonplanar substrates

The structure and device characteristics of InGaAs/GaAs strained quantum wire (QWR) lasers grown by organometallic chemical vapor deposition on 0.25-μm pitch periodic corrugations are reported. The crescent-shaped InGaAs wires, 14–17 nm thick and 70–80 nm in full width, are formed in situ due to surface diffusion of In and Ga species to the bottom of the grating grooves. Room-temperature pulsed operation has been achieved with threshold current densities of 1.9 kA/cm2 for 1.1 mm long lasers with uncoated facets. For laser stripes aligned perpendicular to the wires, the lasing wavelength remains almost constant at 920 nm for temperatures 80<T<150 K due to second-order Bragg reflection from the QWR array. The possibility of achieving gain-coupled distributed feedback using the periodic gain modulation in these devices is discussed.

1-W single-mode edge-emitting DBR ring oscillators

The distributed Bragg reflector (DBR) ring oscillator, a class of single-mode diode laser that emits high-power, spatially coherent, single-frequency output from a large aperture, is discussed. Specifically an edge-emitting DBR ring oscillator that exhibits single frequency operation to 1 W output from a single facet is discussed. From a second device, the far field radiation pattern is a 0.20 degrees diffraction-limited beam which remains stable and stationary up to 460 mW, measured from an uncoated facet. This device produces over 2.5 W of coherent power into four equal beams and has a threshold current density of 177 A/cm/sup 2/ and a differential quantum efficiency of 63%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

InGaAs/GaAs single quantum well lasers with monolithically integrated multilayer wave guides for surface-emitted sum-frequency generation

We report on strained layer InGaAs/GaAs single quantum well (SQW) lasers with monolithically integrated nonlinear wave guides for surface-emitting sum-frequency generation. Broad-area, ridge wave-guide and segmented cavity lasers with uncoated facets were processed from a molecular beam epitaxy grown AlxGa1 − xAs multilayer embedded with an InGaAs SQW separate cofinement heterostructure and tested at room temperature. Broad-area threshold current density of 87.5 A cm−2 was obtained for a cavity length of 3.3 mm and ridge lasers had a minimum threshold current of ~8 mA. The differential internal quantum efficiency, wave-guide loss, and lasing wavelength variation with cavity length were investigated. The sum-frequency generation (SFG) was studied in an active/passive segmented cavity device by coupling 1.06 μm light into the cavity as the transverse magnetic guided wave to interact with the transverse electric SQW laser mode. The measured conversion efficiency in terms of the nonlinear cross section An1 is about 2 × 10−7 W−1, which agrees well with the calculated value. Applications of the integrated devices as WDM demultiplexers and spatially addressable coherent detectors were demonstrated.

Advantages of InGaAsP separate confinement layer in 0.98 μm InGaAs/GaAs/InGaP strained DQW lasers for high power operation at high temperature

The advantages of 0.98 μm InGaAs/GaAs/InGaP lasers with an InGaAsP SCH layer were investigated by comparing them with identical lasers with a conventional GaAs SCH layer. A higher internal quantum efficiency of 0.817 and low internal loss of 2.11 cm−1 were obtained due to the large conduction band discontinuity. Moreover, high power operation of 80 mW from an uncoated facet was obtained up to 70°C with the laser with the InGaAsP SCH layer.

Junction-side up operation of (Al)GaInP lasers with very low threshold currents

Strained (Al)GaInP quantum-well ridge lasers with AlGaAs cladding layers have been fabricated on a 5 degrees -off oriented GaAs substrate. Owing to a heat spreading layer, the devices can be operated junction-side up with a CW threshold current of 13 mA. Singlemode operation is achieved up to power levels of 15 mW for devices with uncoated facets.

Gain and threshold characteristics of strain-compensated multiple-quantum-well lasers

Strain-compensated multiple-quantum-well (MQW) lasers with an operating wavelength near 1.5 mu m have been grown by low-pressure OMVPE. A simple growth method was used to achieve zero net strain structures having InGaAs wells with 1.1% compressive strain and InGaAsP barriers with compensating tension. Broad stripe laser structures with three, six, and nine wells were characterized and the gain coefficient per well is shown to be related to the logarithm of the current density per well. A threshold current density of 451 A/cm/sup -2/ was obtained for a structure with three wells, uncoated facets, and a cavity length of 2 mm. >

Blue and green diode lasers in ZnSe-based quantum wells

Laser diode operation has been obtained from (Zn,Cd)Se/ZnSe and (Zn,Cd)Se/Zn(S,Se) quantum well structures in the blue and the green. The devices, prepared on p- and n-type (In,Ga)As or GaAs buffer layers for lattice matching purposes to control the defect density, have been operated at near-room-temperature conditions and briefly at room temperature with uncoated end facets. Quasi-continuous wave operation has been obtained at T=77 K.

Local mirror temperatures of red-emitting (Al)GaInP quantum-well laser diodes by Raman scattering and reflectance modulation measurements

Temperature rises were measured on cleaved, uncoated mirror facets of junction-side-up mounted (Al)GaInP laser diodes as a function of the injection current by Raman spectroscopy via the Stokes/anti-Stokes phonon line intensity ratio and the phonon line shift as well as by reflectance modulation as a novel application for laser mirror characterization. Below the threshold current the temperature rise is due to Joule heating of the drive current across the ohmic resistor and is ΔT≂35 K at threshold. Above threshold a significant power-dependent heating caused by absorption of laser radiation is superimposed. In this regime the temperature increase is considerably high, i.e., ΔT≥100 K at 4 mW for 5-μm-wide ridge lasers. The different measurement techniques have produced consistent data.

Coupled-stripe in-phase operation of planar native-oxide index-guided AlyGa1−yAs-GaAs-InxGa1−xAs quantum-well heterostructure laser arrays

High-performance, coupled-stripe, planar, index-guided AlyGa1−yAs-GaAs-InxGa1−xAs quantum-well heterostructure (QWH) laser arrays are fabricated by the formation of a relatively thick, current-blocking, native oxide from the high-gap AlyGa1−yAs upper confining layer between active stripes. Precise control of the thickness of the native oxide layer between emitters provides a means of varying the index step between stripes, and permits tailoring of the optical profile to produce in-phase operation. The 10-stripe coupled QWH laser arrays (∼3-μm-wide stripes on 4 μm centers) exhibit near-diffraction-limited, single-lobed, far-field patterns with low continuous (cw) thresholds (∼45 mA) and cw output powers (total external differential quantum efficiency ≳50%) of over 100 mW per uncoated facet.

Blue Lasers Based on II-VI Semiconductor Heterostructures

ABSTRACTProperties of blue laser diodes based on ZnSe-related II-VI semiconductor heterostructures are reported. At 77 K, continuous-wave (cw) operation has been achieved for lasers emitting at wavelengths as short as 470.4 nm (2.635 eV), while pulsed laser emission has been observed up to ∼200 K, for samples with uncoated facets. Measured turn-on voltages for stimulated emission at 77 K were as low as 12 V for some of the laser diodes due to improved ohmic contacts. For some particular devices, differential quantum efficiencies as high as 36% per (uncoated) facet have been obtained at 77 K.

Low-threshold-current-density 1.5 mu m lasers using compressively strained InGaAsP quantum wells

A low-threshold current density (J/sub th/) of 140 A/cm/sup 2/ for broad-area 1.5- mu m semiconductor lasers with uncoated facets is demonstrated at a cavity length of 3.5 mm. This was achieved by the use of a single InGaAsP quantum well (QW) of 1.8% compressive strain inside a step-graded InGaAsP waveguide region. Low-cavity losses of 3.5 cm/sup -1/ and a relatively wide quantum well as compared to InGaAs wells of equivalent strain contribute to this high performance. Double QW devices of 2 mm length showed threshold current densities of 241 A/cm/sup 2/. Quaternary single and double QWs of similar width but only 0. 9% strain gave slightly higher threshold current density values, but allowed growth of a 4 QW structure with a J/sub th/ of 324 A/cm/sup 2/ at L=1.5 mm. >

Visible spectrum native-oxide coupled-stripe In0.5(AlxGa1−x)0.5P–In0.5Ga0.5P quantum well heterostructure laser arrays

Data are presented demonstrating the continuous (cw) operation (10–50 °C) of coupled-stripe In0.5(AlxGa1−x)0.5P–In0.5Ga0.5P multiple quantum well heterostructure (QWH) visible (λ∼655 nm) laser arrays. The ten stripe QWH arrays (3 μm emitters on 4 μm centers) are defined by ‘‘wet’’ oxidation (H2O vapor in N2 carrier gas, 550 °C) of the high gap In0.5(AlxGa1−x)0.5P upper confining layer outside of the active stripes. The gain-guided arrays exhibit relatively low cw 20 °C threshold current densities (∼1.6 kA/cm2, ∼450 μm cavity) and high output powers of 25 mW per uncoated facet (cw, 20 °C). Optical coupling between stripes results in a near diffraction-limited single-lobe far-field pattern indicative of oscillation in the lowest order supermode of the array (in-phase operation).