Novel strained quantum well laser grown by MOVPE

Strained-layer broad-area lasers have been grown by MOVPE. The structures contain 3.5 nm-wide Ga/sub 0.3/In/sub 0.7/As quantum wells. They emit close to 1.5 mu m and have been made to lase under current injection. These structures were compared with similar lasers containing unstrained 7.0 nm-wide Ga/sub 0.47/In/sub 0.53/As quantum wells also emitting at 1.5 mu m. No improvement has been found in J/sub th/ (933 A cm/sup -2/) or T/sub 0/ (47 K) in the case of the strained structure, despite the expected band structure modification.<>     

A novel current injected strained quantum well laser grown by MOVPE

Conventional long wavelength (1.3 and 1.55 μm emitting) GalnAsP alloy lasers suffer from two disadvantages. Firstly, carriers in the highest lying valence band have a heavy effective mass relative to carriers in the conduction band. This asymmetry leads to an increase in the carrier density required for lasing action to occur. Secondly, non-radia-tive recombination processes, such as Auger Recombination (AR) and Inter Valence Band Absorption (IVBA), which involve occupancy of the heavy-hole (HH) states, are thought to be significant in these materials. These again lead to higher thresholds and lower values ofT ₀than might otherwise be the case. Recently, there has been considerable interest in the prospect of “engineering” the band structure of a 1.5 μm emitting device so as to overcome these problems. It has been reported that for a quantum well under biaxial compression, the light-hole/heavy-hole (LH/HH) degeneracy at the gamma point will be lifted such that the highest lying valence band will be LH-like in the in-plane direction. This should reduce both the effective mass asymmetry and the thermal occupancy of the HH states, lowering the threshold carrier density and reducing the AR and IVBA rates. This paper describes MOVPE growth and characterisation of the first 1.55 μm emitting current injected strained layer laser structure. The active region contains 3.5 nm thick strained quantum wells of Ga_o.3In_o.7As situated in the central region of a quaternary waveguide and grown on InP. TEM micrographs and x-ray data demonstrate that the lattice mismatch (approximately 1%) has been accommodated elastically, without the formation of misfit dislocations. Broad area lasers have been fabricated with lengths of 200–1200 μm and threshold current densities as low as 930 Acm^-2 have been measured from the longer devices. Similar 1.55 μm emitting structures containing unstrained 7.5 nm thick Ga_o.47In_o.53As wells have also been grown and characterised for comparison. As yet, no significant improvement in either threshold current orT ₀has been observed for strained lasers over unstrained devices.     

Uniform 90-channel multiwavelength InAs/InGaAsP quantum dot laser

A 93-channel multiwavelength laser with maximum channel intensity non-uniformity of 3.0 dB over a wavelength range from 1638 to 1646 nm was demonstrated on the basis of a single 4500 mum-long InAs/InGaAsP quantum dot Fabry-Perot cavity chip. All channels were stable because of inhomogeneous gain broadening due to statistically distributed sizes and geometries of self-assembled quantum dots     

Optical characterisation of MOVPE grown vertically correlated InAs/GaAs quantum dots

Structures with vertically correlated self-organised InAs quantum dots (QDs) in a GaAs matrix were grown by the low-pressure metal-organic vapour phase epitaxy (MOVPE) and characterised by different microscopic techniques. Photoluminescence in combination with photomodulated reflectance spectroscopy were applied for characterisation of QDs structures. We show that combination of both methods allows detecting optical transitions originating both from QDs and wetting (separation) layers, which can be than compared with those obtained from numerical simulations. On the basis of obtained results, we demonstrate that photoreflectance spectroscopy is an excellent tool for characterisation of QDs structures wetting layers and for identification of spacer thicknesses in vertically stacked QDs structures.     

Optical and structural properties of MOVPE grown GaxIn1−xAs/InP strained multiple quantum well atructures

This paper presents a study of the structural and optical properties of strained GaInAs/ InP multiple quantum well (MQW) structures fabricated by LP-MOVPE. The composition of the Ga _x In_1−x As films ranged fromx = 0.17 tox = 1.0 and was determined by sputtered neutral mass spectrometry (SNMS) on thick layers. The structures of the MQW samples with well widths from 1.5 to 5 nm were investigated by high resolution x-ray diffraction (HR-XRD). Simulations of the diffraction patterns showed that transition layers of approximately 2 monolayer (ML) thickness with high lattice mismatch exist at the interfaces. Photoluminescence (PL) measurements indicate well widths of a multiple of a monolayer with local variations of one monolayer. The PL peak energies vary smoothly with the Ga concentration. These results were confirmed by optical absorption measurements.     

Wide-temperature-range operation of 1.3-/spl mu/m beam expander-integrated laser diodes grown by in-plane thickness control MOVPE using a silicon shadow mask

A new fabrication method of high-quality thickness-tapered semiconductor waveguides is proposed based on controlling in-plane thickness during MOVPE by using a comb-shaped silicon shadow mask. It was used to fabricate a 1.3-/spl mu/m-wavelength narrow-beam (less than 13/spl deg/) InGaAsP-InP laser diode, which achieved high-power (over 20 mW) operation up to 85.     

AlGaN/GaN high electron mobility transistors with selective area grown p-GaN gates

We report a selective area growth (SAG) method to define the p-GaN gate of AlGaN/GaN high electron mobility transistors (HEMTs) by metal-organic chemical vapor deposition. Compared with Schottky gate HEMTs, the SAG p-GaN gate HEMTs show more positive threshold voltage (V_th) and better gate control ability. The influence of Cp₂Mg flux of SAG p-GaN gate on the AlGaN/GaN HEMTs has also been studied. With the increasing Cp₂Mg from 0.16 μmol/min to 0.20 μmol/min, the V_th raises from -67 V to -37 V. The maximum transconductance of the SAG HEMT at a drain voltage of 10 V is 113.9 mS/mm while that value of the Schottky HEMT is 51.6 mS/mm. The SAG method paves a promising way for achieving p-GaN gate normally-off AlGaN/GaN HEMTs without dry etching damage.     

Preliminary comparison of ballistic electron emission spectroscopy measurements on InAs quantum dots in a GaAs/AlGaAs heterostructure grown by MBE and MOVPE

Self-assembled InAs quantum dots (SAQDs) in GaAs/GaAlAs structures grown by molecular beam epitaxy (MBE) and metal-organic vapour phase epitaxy (MOVPE) of similar size was examined by ballistic electron emission spectroscopy. Ballistic current-voltage characteristics through the QD in the voltage range from 0.55 to 0.9 V (range where the presence of resonance states of QD is expected) with its derivative (the derivation of the spectroscopic characteristics represents quantum levels in the QD) are given. Differences in the intensities and sharpnesses of the QD levels for MBE and MOVPE grown QDs are observed.     

Increasing the quantum efficiency of InAs/GaAs QD arrays for solar cells grown by MOVPE without using strain‐balance technology

Research into the formation of InAs quantum dots (QDs) in GaAs using the metalorganic vapor phase epitaxy technique is presented. This technique is deemed to be cheaper than the more often used and studied molecular beam epitaxy. The best conditions for obtaining a high photoluminescence response, indicating a good material quality, have been found among a wide range of possibilities. Solar cells with an excellent quantum efficiency have been obtained, with a sub‐bandgap photo‐response of 0.07 mA/cm² per QD layer, the highest achieved so far with the InAs/GaAs system, proving the potential of this technology to be able to increase the efficiency of lattice‐matched multi‐junction solar cells and contributing to a better understanding of QD technology toward the achievement of practical intermediate‐band solar cells. Copyright © 2016 John Wiley & Sons, Ltd.     

Multiwavelength, densely-packed 2/spl times/2 vertical-cavity surface-emitting laser array fabricated using selective oxidation

Data are presented characterizing an individually addressable, multiwavelength 2/spl times/2 vertical-cavity surface-emitting laser array. The individual elements are fabricated on center-to-center spacings of 12 /spl mu/m with the lasing wavelengths controlled through the selectively oxidized lateral device sizes. Devices sized 3.5, 3.0, 2.5, and 2.0 /spl mu/m result in lasing wavelengths of 9608, 9598, 9587, and 9574 /spl Aring/, respectively. Continuous wave threshold currents of the four elements with decreasing device sizes are 240, 214, 187, and 169 /spl mu/A, respectively.     

1.3 /spl mu/m GaAs/GaAsSb quantum well laser grown by solid source molecular beam epitaxy

A highly strained GaAs/GaAs/sub 0.64/Sb/sub 0.36/ single quantum well laser has been grown on GaAs (100) substrate by using solid source molecular beam epitaxy. The uncoated broad-area laser demonstrates 1.292 /spl mu/m pulsed operation with a low threshold current density of 300 A/cm/sup 2/. The spontaneous emission of the laser was also studied. The result reveals that the Auger recombination component dominates the threshold current at high temperature.     

Vertically compact 15 GHz GaAs/AlGaAs multiple quantum well laser grown by molecular beam epitaxy

A GaAs/Al/sub x/Ga/sub 1-x/As multiple quantum well laser with an electrical modulation bandwidth exceeding 15 GHz has been fabricated. Optimised design of the waveguide, including development of high Al mole fraction (x=0.8) cladding layers, together with a coplanar electrode geometry, has resulted in a vertically compact laser structure suitable for integration.<>     

Low drive voltage (1.5 Vp.p.) and high power DFB-LD/modulatorintegrated light sources using bandgap energy controlled selective MOVPE

The authors have reduced modulator drive voltage in DFB-LD/modulator integrated light sources (DFB/MODs) taking fabrication tolerance into account. By enhancing the quantum confined Stark effect through well width increase and optimising the doping profile, DFB/MODS with >13 dB extinction ratio at 1.5 V and >4 mW (+6 dBm) output power at 100 mA were achieved while maintaining a reasonably large fabrication tolerance     

Real-time imaging using a 4.3-THz quantum cascade laser and a 320 /spl times/ 240 microbolometer focal-plane array

We report the use of a /spl sim/50-mW peak power 4.3-THz quantum cascade laser (QCL) as an illumination source for real-time imaging with a 320 /spl times/ 240 element room-temperature microbolometer focal-plane array detector. The QCL is modulated synchronously with the focal-plane array for differential imaging. Signal-to-noise ratios of /spl sim/340 are achieved at a 20-frame/s acquisition rate, and the optical noise equivalent power of the detector array at 4.3 THz is estimated to be /spl sim/320 pW//spl radic/Hz. Both reflection and transmission mode imaging are demonstrated.     

Study of metamorphic InGaAs/GaAs quantum well laser materials grown on GaAs substrate by molecular beam epitaxy

The GaAs based InGaAs metamorphic structures and their growth by molecular beam epitaxy (MBE) are investigated. The controlling of the source temperature is improved to realize the linearly graded InGaAs metamorphic structure precisely. The threading dislocations are reduced. We also optimize the growth and annealing parameters of the InGaAs quantum well (QW). The 1.3-μm GaAs based metamorphic InGaAs QW is completed. A 1.3-μm GaAs based metamorphic laser is reported.     

The effects of laser irradiation on InGaAs/GaAs multiple quantum wells grown by metalorganic molecular beam epitaxy

We studied the effects of Ar ion laser irradiation during the growth of InGaAs/ GaAs multiple quantum wells (MQW) structures by metalorganic molecular beam epitaxy. Structural and optical properties were characterized by Nomarski microscopy, Dektak stylus profiler, and low-temperature photoluminescence (PL) measurements. For MQW structures grown at a relatively low substrate temperature (500°C), the laser irradiation influences greatly the growth process of the In^Ga^^As well and results in a large blue shift of about 2000à in the PL peak. Such a large blue shift suggests that laser modification during growth could have some novel applications in optoelectronics. On the other hand, the laser irradiation has relatively small effects on samples grown at a higher substrate temperature (550°C).     

Optical and morphological properties of In(Ga)As/GaAs quantum dots grown on novel index surfaces

Optical and morphological properties of self assembled In(Ga)As/GaAs quantum dot systems, grown on high index (N11) substrates, for a wide range of orientations, coverages and compositions, are presented and reviewed. The use of high Miller index substrate orientations permits to intervene on major quantum dots properties such as shape, size distribution, transition energy and emission polarisation, thus opening a wide range of device design opportunities.     

Preliminary reliability studies of 1.55 mu m graded index separate confinement buried heterostructure (GRINSCH) multiple quantum well (MQW) lasers grown by metalorganic vapour phase epitaxy (MOVPE)

1.55 mu m graded index separate confinement heterostructure (GRINSCH) multi-quantum-well (MQW) lasers, grown entirely by metalorganic vapour phase epitaxy (MOVPE), have demonstrated low degradation rates in lifetests at 50 degrees C, 4 mW per facet. These lasers are complex structures, containing many interfaces, and the encouraging early lifetest results demonstrate the ability of MOVPE to grow these structures.<>     

Low threshold current density 1.5 mu m GaInAs/AlGaInAs graded-index separate-confinement-heterostructure quantum well laser diodes grown by metal organic chemical vapour deposition

A low threshold current density of 640 A/cm/sup 2/ was obtained in a 1.5 Gmm GaInAs/AlGaInAs multiple quantum well laser diode, grown by metal organic chemical vapour deposition, with continuously graded-index separate-confinement heterostructure. An internal waveguide loss of 14 cm/sup -1/ and internal quantum efficiency of 59% were obtained, which are comparable to those of GaInAs/GaInAsP quantum well laser diodes.<>     

1.3 mu m GaInAsP/InP buried heterostructure graded index separate confinement multiple quantum well (BH-GRIN-SC-MQW) lasers entirely grown by metalorganic chemical vapour deposition (MOCVD)

Reports the first successful demonstration of a 1.3 mu m GaInAsP/InP buried heterostructure graded index separate confinement multiple quantum well laser (BH-GRIN-SC-MQW LD) entirely grown by three-step low pressure metal-organic chemical vapour deposition (LP-MOCVD). The threshold current and the differential quantum efficiency were 31 mA (threshold current density 3.4 kA/cm/sup 2/) and 28%/facet, respectively. A characteristic temperature of 65 K was obtained.<>