Graded Index Separate Confinement Heterostructure Research Articles

Periodic index separate confinement heterostructure InGaAs/AlGaAs multiple quantum well laser grown by organometallic vapor phase epitaxy

Organometallic vapor phase epitaxy was used to grow a novel periodic index separate confinement heterostructure (PINSCH) InGaAs/AlGaAs multiple quantum well (MQW) laser. Secondary ion mass spectrometry and transmission electron microscopy were used to characterize the structure. The performance of the PINSCH laser was compared with that of a graded index separate confinement heterostructure (GRINSCH) MQW laser grown under similar conditions. The PINSCH laser uses cladding layers comprised of periodic semiconductor multilayers (Al0.4Ga0.6As/GaAs) which provide both optical and electrical confinement. Since the optical field decays over several multilayers, and therefore is far less tightly confined than in the GRINSCH structure, a significant reduction of the transverse far-field angle occurs. Comparing the performance of 5×750 μm self-aligned ridge waveguide InGaAs/AlGaAs lasers emitting at 980 nm, the PINSCH structure exhibits a transverse far-field angle of 23° compared to 46° for the GRINSCH. This is obtained at the expense of a modest increase in threshold current (19 mA vs 10 mA).

A novel technique for low-threshold and high-power InGaAs/GaAs strained-layer 0.98-μm buried heterostructure laser fabrication

A novel fabrication technique has been developed for InGaAs/GaAs strained-layer buried heterostructure lasers. Dielectric masks and Zn diffusion are not required in this technique. This novel fabrication process is much easier than the conventional approach and yields excellent laser results. A low threshold of 3 mA and high-power operation for lasing wavelength of 9800±20 Å have been achieved with graded index separate confinement heterostructure devices using this novel technique.

Interface traps and interface recombination in AlGaAs/GaAs quantum well laser diodes

The current-voltage characteristics and deep traps of various GaAs/AlGaAs graded-index separate confinement heterostructure quantum well laser diode structures are studied as a function of the growth temperature and threshold current. It is shown that the interface nonradiative recombination processes cause a high threshold current. An impurity-related deep level with activation energy Ea=0.48 eV at the interface region and an interface state with wide energy distribution were found in the high threshold current diodes. The current-voltage characteristics show that interface recombination, rather than bulk recombination, is the dominant carrier transport process in the diodes and is responsible for the high threshold current.

(InAs)1/(GaAs)n Superlattice Quantum Well Lasers

Strained layer In0.2Ga0.8As/GaAs quantum-well (QW) lasers have been used to pump Erbium Doped Fiber Amplifiers for use in opto-electronic communication systems. These InGaAs/GaAs Q-W lasers grown as graded index separate confinement heterostructures (GRINSCH) emit at 980 nm and have exhibited low threshold current densities, high electrical to optical power conversion efficiencies, low noise, and low temperature sensitivities [1–3]. Recently there has been much attention toward the growth and fabrication of devices containing short period superlattices of (InAs)m/(GaAs)m or (GaAs)m/(AlAs)n compositions [4–9]. Indeed the growth of inverted MODFET structures using a (GaAs)/(AlAs) superlattice barrier in place of an AlGaAs random alloy exhibited an increase in low temperature mobility due to reductions in the number of impurities and interface roughness [7]]. Can the optical properties of strained layer InGaAs/GaAs Q-W lasers also be improved by growing an (InAs)/(GaAs)4 short period superlattice as the active layer in place of the In0.2Ga0.8 As random alloy?This paper reports the fabrication of ridge waveguide lasers using a 6 period (InAs)1/(GaAs)4 superlattice active region in a GRINSCH laser structure. One period of the superlattice consists of 1 monolayer (ML) of InAs and 4 ML of GaAs. Thus the average In composition in the superlattice is 20%. This superlattice laser is an alternative to the In0.2Ga0.8As/GaAs random alloy quantum-well laser used as a pump source for Erbium Doped Fiber Amplifiers. In a single quantum well In0.2Ga0.8As/GaAs laser the active region is a thin layer (-70Å thick) sandwiched between GaAs barrier layers. The superlattice active laser reported here has 6 periods of (InAs)1/(GaAs)4 as the light emitting region of a total width comparable to a single quantum well of random alloy composition.

Fabrication of 780-nm AlGaAs Tunable Distributed Bragg Reflector Laser Diodes by Using Compositional Disordering of a Quantum Well

AlGaAs tunable distributed Bragg reflector (DBR) laser diodes (LD's) with a lasing wavelength of 780 nm were fabricated by means of electron beam (EB) lithography, ion implantation, and two-step metalorganic vapor phase epitaxy (MOVPE). Active and passive waveguides were monolithically integrated by using silicon ion implantation for compositional disordering of quantum-well heterostructures. The optimum single-quantum-well (SQW) structure, with low threshold current and low internal loss, is about 5 nm thick and has an Al mole fraction of 0.06. The graded-index separate-confinement heterostructure (GRIN-SCH) with a carrier-blocking layer was also used to improve the characteristic temperature of a two-step-growth LD. A Iinewidth as narrow as 690 kHz and a frequency tuning of more than 1.7 THz were obtained.

Optical and RF characteristics of short-cavity-length multiquantum-well strained-layer lasers

The optical and RF characteristics of short-cavity, strained-layer In/sub 0.3/Ga/sub 0.7/As graded-index separate-confinement-heterostructure (GRINSCH) multiple-quantum-well ridge waveguide lasers are described. Short-cavity-length strained-layer lasers with four In/sub 0.3/Ga/sub 0.7/As quantum wells have been fabricated using chemically assisted ion beam etching (CAIBE). These lasers have a very low K factor of 0.14 ns and a high differential gain of 1.1*10/sup -15/ cm/sup 2/. A 3 dB modulation bandwidth of 23.5 GHz has been measured on a 50 mu m cavity-length device. This is the highest reported bandwidth for a quantum well laser. >

High-temperature operation of periodic index separate confinement heterostructure quantum well laser

High-temperature operation of the InGaAs/GaAs/AlGaAs quantum well lasers with an expanded vertical optical mode is demonstrated for the first time using a periodic index separate confinement heterostructure (PINSCH) laser. Continuous wave (cw) operation up to 145 °C is achieved with a coated 3 μm×508 μm PINSCH laser. The measured characteristic temperature (170 K) and external differential quantum efficiency (0.75 mW/mA) are comparable to those obtained in a graded index separate confinement heterostructure laser fabricated at the same time. These results illustrate the excellent capability of the PINSCH laser to compress the transverse beam divergence without sacrificing the electrical carrier confinement.

Carrier heating in AlGaAs single quantum well laser diodes

The nonamplified spontaneous emission of AlGaAs single quantum well graded index separate confinement heterostructure laser diodes has been measured for photon energies between 1.35 and 2.05 eV and at pump currents up to 19 kA cm−2 and optical flux densities up to 35 MW cm−2. The spectra are very complex and we observe the following three features. First, the spontaneous emission intensity increases slowly with current, even above threshold. Second, the carrier temperature increases slightly above the lattice temperature, 28 K at a pump rate of 1.5×1029 cm−3 s−1. Third, at high power densities the high-energy spontaneous emission at a photon energy of 1.9 eV increases dramatically.

1W CW, 672 nm visible laser diodes

Visible laser diodes emitting at 672 nm and employing a GaInP strained-layer, single quantum well, graded-index separate confinement heterostructure (GRINSCH) design have been fabricated. CW output power in excess of 1 W and CW threshold current density as low as 305 A/cm2 were obtained from a coated, 60 μm wide oxide stripe diode operating at 10°C.

GaAs-based diode lasers on Si with increased lifetime obtained by using strained InGaAs active layer

Strained InGaAs/AlGaAs quantum well diode lasers have been fabricated on Si substrates for the first time. A GaAs buffer layer was grown on each Si wafer by temperature-cycled organometallic vapor phase epitaxy (OMVPE). The wafer was then transferred to a second reactor for OMVPE growth of a graded-index separate-confinement heterostructure single-quantum well laser structure. For lasers with a cavity length of 1000 μm, room-temperature pulsed threshold current densities as low as 174 and 195 A/cm2 have been obtained for active layer compositions of In0.02Ga0.98As and In0.05Ga0.95As, respectively. One laser with an In0.05Ga0.95As active layer operated cw for 56.5 h, a record lifetime for GaAs-based diode lasers on Si.

Full-wafer technology for large-scale laser processing and testing

A new approach for large-scale semiconductor laser fabrication is presented. In this ‘‘full-wafer processing and testing’’ concept, the mirrors are fabricated, not by cleaving the wafer but by forming them by means of a chemically assisted ion beam etching process. This allows for on-wafer mirror passivation and testing of the finished devices. Full-wafer technology changes the traditional way of discrete device fabrication and testing to a method more akin to today’s very large-scale integrated (VLSI) technology. Consequently, it provides similar advantages in cost and throughput. Additionally, it allows other electrical and electro-optical device components to be monolithically integrated on the wafer. Currently, we are routinely fabricating AlGaAs/GaAs diode lasers with a single quantum well graded index separate confinement heterostructure (SQW-GRINSCH)-type ridge structure using full-wafer technology. Such lasers exhibit excellent beam properties in single mode up to at least 50 mW output power. Their functional characteristics are indistinguishable from comparable lasers with cleaved facets obtained from the same wafer for comparison purposes. This result reflects the high quality of the etched mirrors. Typically, their surface roughness is less than 200 Å, with mirror reflectivities of about 30% and losses due to mirror scattering below 2%. Having functional parts on the uncleaved wafer allows automated full-wafer testing that encompasses wafer characterization and part screening. This not only eliminates part handling, with its associated yield loss, it also permits a much expanded scope of testing in a fraction of the time previously required.

Etched-facet AlGaAs triangular-shaped ring lasers with output coupling

Total and partial reflection are demonstrated at the bends of V-shaped lasers. By varying the angle of incidence to the facet at the bend, the reflectivity at this facet can be changed. Two totally and one partially reflecting V-shaped lasers are combined in a unibodied structure to realize a triangular-shaped ring laser (trilaser). Trilasers are made of three sections which meet at three facets. Two of the facets provide total internal reflection while the third allows partial transmission from which light output is obtained. The Q of the resultant planar cavity is modified by geometry, without the need for facet coating. V-shaped lasers and trilasers are formed by using the chemically assisted ion beam etching technique in an AlGaAs/GaAs-based single quantum well graded-index separate confinement heterostructure material.

Revealing process-induced strain fields in GaAs/AlGaAs lasers via electron irradiation in a scanning electron microscope

An electron beam induced current study has been performed on single quantum well graded index separate confinement heterostructure GaAs/AlGaAs ridge geometry lasers. It has been shown that electron irradiation in the keV range combined with the electron beam induced current technique can be used to reveal process-induced strain fields and to study strain-related degradation phenomena in these devices on a microscopic scale. This technique has revealed a strain field below the ridge and below an opening in the metal layer. Enhanced susceptibility to degradation processes has been detected close to the lower corners of the ridge. It is shown that a correct interpretation of electron beam induced current images requires, including as contrast mechanism, local fluctuations in the distribution of the electric potential in the device and capture properties of quantum wells; (in the past, electron beam induced current images of degraded lasers were interpreted under the assumption that the contrast reflects the distribution of defects which act as recombination centers). A possible role of process-induced strain fields in the formation of fluctuations in the material’s built-in electric potential distribution within the active part of the laser during degradation is discussed.

Low-threshold CW operation of square-shaped semiconductor ring lasers (orbiter lasers)

The CW operation of square-shaped semiconductor ring lasers is demonstrated with a threshold current as low as 6 mA. The ring resonator consists of straight waveguides and four total reflection mirrors. The lasers are fabricated using Br/sub 2/ dry etching on an InGaAs/GaAs strained single-quantum-well graded-index separate-confinement heterostructure wafer. The low-threshold CW operation is due to the high differential gain of the wafer and the low-loss total reflection mirror.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-threshold GaAs/AlGaAs quantum-well lasers grown by organometallic vapor-phase epitaxy using trimethylamine alane

We have utilized a new aluminum source, trimethylamine alane (TMAA), in the growth of graded-index separate-confinement heterostructure single quantum-well GaAs/AlGaAs laser structures by low pressure (30 Torr) organometallic vapor-phase epitaxy. We find lower carbon and oxygen incorporation in AlGaAs epilayers using TMAA since it does not contain a direct Al–C bond and it is not susceptible to the formation of volatile Al–O containing compounds. The oxygen and carbon concentrations were below the detection limits (&amp;lt; 5 × 1016 cm−3 and &amp;lt; 3 × 1016 cm−3, respectively) of the secondary ion mass spectrometry measurements. Broad-area lasers with 10-nm quantum wells and Al0.45Ga0.55As cladding layers exhibited threshold current densities of 140 A cm−2 for cavity lengths of 1 mm, internal quantum efficiencies of 81%, and intrinsic losses of 1.6 cm−1. These results demonstrate that extremely high-quality AlGaAs and GaAs quantum wells can be grown with TMAA.

Very low threshold single quantum well graded-index separate confinement heterostructure InGaAs/InGaAsP lasers grown by chemical beam epitaxy

We have succeeded in preparing 1.5 μm wavelength strained-layer graded-index separate confinement heterostructure (GRINSCH) InGaAs/InGaAsP single quantum well (SQW) injection lasers by chemical beam epitaxy (CBE). These lasers have extremely low threshold current density Jth of 170 A/cm2, internal quantum efficiency of 83%, and internal waveguide loss of 3.8 cm−1. To the best of our knowledge, these results represent the best values obtained thus far from long-wavelength InGaAs/InGaAsP quantum well injection lasers grown by any techniques. However, despite the recent rapid reduction in Jth, the threshold-temperature dependence remains poor (T0=45 K) even in these very low Jth GRINSCH SQW lasers.

High-power, very low threshold, GaInP/AlGaInP visible diode lasers

Visible light (665 nm) laser diodes employing a strained-layer, single quantum well, graded index separate confinement heterostructure were fabricated from epitaxial wafers grown by metalorganic chemical vapor deposition. Threshold current densities for single element, uncoated, broad-area diodes operated cw as low as 425 A/cm2, cw power outputs of 340 mW per facet, and pulsed outputs (100 μs pulse width) of slightly under 1 W per facet were achieved. These power output values are believed to be the highest reported to date for visible light diode lasers, and this cw threshold current density is believed to be, by far, the lowest.

Very high-power (425 mW) AlGaAs SQW-GRINSCH ridge laser with frequency-doubled output (41 mW at 428 nm)

A very high-power AlGaAs single-quantum-well graded-index separate confinement heterostructure (GRINSCH) ridge laser operating in a diffraction-limited fundamental transverse mode up to 360 mW at a wavelength of 856 nm is presented. The maximum power output of the laser reached 425 mW, limited by thermal saturation of the device and not by catastrophic optical mirror damage. These lasers exhibit very high power levels and show excellent reliability at high output power levels. The extremely high, continuous-wave (CW) fundamental mode power combined with very low-intensity and optical phase distortion as well as low astigmatism render this ridge waveguide laser suitable for optical storage systems, printers, and direct frequency doubling. These devices have been successfully used for direct-frequency doubling of their output in a resonant KNbO/sub 3/ cavity yielding 41 mW of blue radiation at 428 nm. >

Characteristics of coherent two-dimensional grating surface emitting diode laser arrays during CW operation

Recent progress in the development of monolithic two-dimensional coherent grating surface emitting (GSE) laser arrays is presented. Such GSE arrays have operated continuously to more than 3 W/surface and pulsed to more than 30 W/surface. They have achieved continuous wave (CW) threshold current densities of under 140 A/cm/sup 2/ with CW differential quantum efficiencies of 20-46% per surface. Linewidths in the 40-100 MHz range were obtained with output powers of 100-300 mW per surface. The arrays typically consist of 10-30 mutually injection coupled gain sections with 10 laterally coupled ridge-guided lasers in each gain section. A single GaInAs strained-layer quantum well with a graded-index separate confinement heterostructure (GRINSCH) geometry allows junction down mounting with light emission through the transparent GaAs substrate. A surface relief grating is used for feedback and outcoupling.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Indium migration and controlled lateral bandgap variations in high-power strained layer InGaAs-AlGaAs lasers grown on nonplanar substrates

Strained single quantum well (SQW) InGaAs-AlGaAs graded-index separate confinement heterostructure (GRINSCH) lasers were grown by molecular beam epitaxy over nonplanar