Fabrication and characteristics of ion beam etched cavity InP/InGaAsP BH lasers

A low temperature ion beam etching (IBE) process is successfully applied to facet mirror fabrication of 1.3 μm InGaAsP/InP buried heterostructure (BH) lasers. Ar ion beam etching characteristics of InP are studied and masking conditions are optimized for obtaining low-damage, vertical, and smooth etched facets. Lasers fabricated by this technique have threshold currents and quantum efficiencies comparable to those of lasers with conventionally cleaved mirrors. CW operation at room temperature has been achieved. Initial experimental results of preliminary aging tests are also presented.     

CW operation of 1.5 ?m InGaAsP/InP BH lasers with a reactive-ion-etched facet

The reactive-ion-etching (RIE) technique utilising a TiO2 mask and Cl2-Ar gas is successfully applied to facet mirror fabrication of 1.5 ?m InGaAsP/InP buried-heterostructure (BH) lasers. Room-temperature CW operation has been achieved with a structure having one etched and one cleaved facet. A threshold current value of 30 mA at 25°C has been achieved for a laser with a 380 ?m cavity length.     

Low threshold GaAs/GaAlAs BH lasers with ion-beam-etched mirrors

We report the use of the ion-beam etching (IBE) technique to produce GaAs/GaAlAs BH lasers with one etched and one cleaved mirror facet. Low threshold currents of 12 mA have been measured in devices with 100 ?m-long cavities.     

GaAs integrated optical circuits by wet chemical etching

An integrated optical circuit containing a laser, passive waveguide, and extra-cavity detector is described. These devices are fabricated from AlxGa1-xAs layers grown by liquid-phase epitaxy. Reflectors are formed by a two-step preferential etch procedure. For proper laser orientation on {100} wafers, the mirrors are found to be oblique, tapered so as to enhance coupling into the underlying passive waveguide; this increases the efficiency of radiation transfer to the detector. Device operation with high differential transfer efficiency and low threshold has been achieved; e.g., for devices with one etched mirror and one cleaved mirror, ηt= 16 percent andJ_{t} = 2.4kA/cm², whereas these values areeta_{t} = 6.5percent and Jt= 3.0 kA/cm²for devices with two etched mirrors. Other orientations on {100} and {110} wafers have also been investigated. The reflectivity of the etched mirrors is small,R_{e} simeq 1-2percent, but transfer efficiencies into the external passive waveguide as large asT = 50percent have been observed. The effect of small Reon device performance is examined both experimentally and theoretically. The fabrication of ribbed interconnections between active circuit components is also described.     

Three- and four-layer LPE InGaAs(P) mushroom stripe lasers for λ = 1.30, 1.54, and 1.66 µm

Mushroom stripe (MS) InGaAsP/InP and InGaAs/InP lasers have been realized emitting atlambda = 1.3, 1.54,and 1.66 μm, respectively. The main advantage of these MS lasers is their technological simplicity, because only one epitaxial growth step consisting of three or four layers, respectively, is required. No contact layer and no filling layers are needed. In our phosphorus silicate glass (PSG) passivated MS lasers, current spreading is completely inhibited. The devices have very low CW threshold currents and high values of output power, external differential efficiency, and To. All these properties are equivalent to those of the much more complicated buried heterostructure lasers. CW operation in up-side-up mounted MS lasers on p-type substrates is easily achieved, because their series resistance is very low. The devices oscillate in the fundamental lateral mode for easily achievable width and thickness combinations, and tend to longitudinal monomode behavior at moderate output powers. The modulation capability is more than 1 Gbit/s RZ due to the low capacitance of the mushrooms. The commonly used antimeltback layer for lasers withlambda > 1.5 mum on     

An AlGaAs laser with high-quality dry etched mirrors fabricatedusing an ultrahigh vacuum in situ dry etching and deposition processingsystem

Highly reliable AlGaAs lasers with dry etched mirrors have been successfully fabricated with an ultrahigh-vacuum in situ processing system, equipped with reactive ion-beam etching (RIBE) and dielectric film deposition chambers. Etched mirror surfaces are protected against air-exposure contamination and nonvolatile-reaction-products adsorption with in situ Al₂O₃ passivation subsequent to the CI₂ RIBE mirror formation. Ion-bombardment-induced damage is repaired by thermal annealing. The annealing effect is enhanced by a contamination-free interface between the etched mirror surface and Al ₂O₃ passivation film. The lasers exhibit an increase in catastrophic optical damage (COD) level and long-life operation. Their COD levels are twice as high as that for as-etched lasers and are almost the same as those for conventional cleaved lasers     

Room temperature CW operation of GaInAsP/InP double heterostructure diode lasers emitting at 1.5 ?m grown by low pressure metalorganic chemical vapour deposition (LP-MO CVD)

Room temperature continuous wave (CW) operation at 1.5 ?m has been achieved in GaInAsP/InP DH lasers fabricated on material grown by low-pressure metalorganic chemical vapour deposition (LP-MO CVD). Threshold currents as low as 200 mA DC have been measured for devices with a stripe width of 9 ?m and a cavity length of 300 ?m. Values of To as high as 64 K have been obtained, where To is defined by the expression Jth(T) = Jth(0) exp (T/To). Fundamental transverse mode oscillation has been achieved up to an output power of 10 mW.     

Integration of a laser diode with a polymer-based waveguide forphotonic integrated circuits

The fabrication and characterization of BRS lasers monolithically integrated with butt-coupled polymer-based buried strip waveguides is presented. Threshold currents of lasers with one cleaved and one etched mirror facets are 15-18 mA and waveguide output powers are in excess of 5 mW at 100 mA laser driving currents and for 600 μm long waveguides. The device exhibits a total waveguide insertion loss less than 5 dB. The integrated device is potentially suitable as a building-block for photonic integrated circuits     

Monolithic integration of curved waveguides and channeled-substrate DH lasers by wet chemical etching

Integration of AlGaAs/GaAs curved waveguides and other two-dimensional waveguides with DH lasers and detectors is demonstrated. Devices are fabricated from LPE AlGaAs/GaAs layers by wet chemical etching processes. Differential transfer efficiencies ofeta_{t}= 5percent are routinely achieved in a structure consisting of an integrated laser, a 90° curved waveguide with 150μm radius, and a detector, for the case where one laser mirror is etched and one cleaved. This value iseta_{t}= 4percent if both mirrors are etched. A comparison of waveguide attenuation between straight and curved rib waveguides is given, along with the transfer characteristics of curved waveguides. The loss coefficient of curved rib waveguides with 150-μm radius is about two times that of a straight waveguide of the same length. The fabrication and properties of channeled-substrate crescent (CSC) lasers and detectors with transverse single-mode confinement, monolithically integrated by means of passive CSC interconnecting waveguides, is also described.     

Zn-diffused, stripe-geometry, double-heterostructure GaInAsP/InP diode lasers

Deep Zn diffusion from a ZnP2source has been used to fabricate stripe-geometry double-heterostructure GaInAsP/InP diode lasers with emission wavelengths in the1.2-1.3 mum range. These devices exhibit good electrical and optical confinement. For sufficiently narrow stripe widths (<10 mum), emission is usually single mode and linear. CW outputs up to ∼8 mW per facet have been observed. In initial life tests, two Zn-diffused lasers have operated CW at room temperature for over 5000 h without appreciable degradation.     

GaInAsP/InP DH lasers with a chemically etched facet

We describe a new configuration and novel fabrication method for GaInAsP/InP DH lasers in which one of the facet mirrors is chemically etched and the other one is formed by cleaving. The etched facet is fabricated monolithically by wet chemical etching in a solution of HCl:CH3COOH:H2O2= (1:2:1). Broad-area contact lasers of this type operating at room temperature at a wavelength ofsim 1.3 mum have been demonstrated.     

Threshold current analysis of compressive strain (0-1.8%) inlow-threshold, long-wavelength quantum well lasers

A comprehensive study of the effect of compressive strain on the threshold current performance of long-wavelength (1.5 μm) quantum-well (QW) lasers is presented. Model predictions of threshold currents in such devices identify QW thickness as a parameter that must be considered in optimizing laser performance when Auger currents are present. Experimental comparisons between strained and unstrained devices reveal strain-induced reductions in internal transparency current density per QW from 66 to 40 A/cm², an increase in peak differential modal gain from 0.12 to 0.23 cm/A, and evidence for the elimination of intervalence band absorption as compressive strain increases from 0 to 1.8%. However, most of these improvements arise in the first ~1% of compressive strain. To fabricate low-threshold 1.5-μm buried heterostructure (BH) devices in InP using the strained QW active regions an optimized design which shows that threshold current is at its lowest when the stripe width is approximately 0.6-0.7 μm is derived. Results for uncoated BH lasers are reported     

Room-temperature pulsed operation of triple-quantum-well GaInNAslasers grown on misoriented GaAs substrates by MOCVD

The lasing operation of three-quantum-well GaInNAs stripe geometry lasers grown by MOCVD on 0° and 6° misoriented (100) GaAs substrates, respectively, have been demonstrated and their performance is compared for the first time. Both devices achieved room temperature, pulsed lasing operation at an emission wavelength of 1.17 μm, with a threshold current density of 667 A/cm² for lasers grown on 6° misoriented substrates, and 1 kA/cm² for lasers grown on 0° misoriented substrates. The threshold for the lasers grown on 6° misoriented substrates compares favorably with the best results for GaInNAs lasers. Lasers with narrower stripe width and a planar geometry have also been demonstrated by the use of lateral selective wet oxidation for current confinement, with a threshold current density of 800 A/cm² for 25-μm-wide devices     

1.3-μm AlGaInAs buried-heterostructure lasers

1.3-μm AlGaInAs-InP strained multiple-quantumwell (MQW) buried-heterostructure (BH) lasers have been successfully fabricated. InP current blocking layers could be smoothly regrown using the simple HF pretreatment, although the etched active region includes Al-containing layers. The threshold current I_th was typically 11 mA for as-cleaved 350-μm-long devices, which is about 30% lower than that of the ridge laser counterparts. A maximum continuous-wave operating temperature as high as 155°C was achieved. For the 200-μm-long device with the high-reflective-coated rear-facet, I_th was as low as 7.5 mA and characteristic temperature T₀ was 80 K. The BH lasers also provided more circular far-field patterns and lower thermal resistances than for ridge lasers     

GaInAsP/InP laser with monolithically integrated monitoring detector

Monolithic fabrication of a GaInAsP/InP laser with an etched mirror and monitoring detector is reported. Stripegeometry lasers operating at wavelengths of ~1.3 ?m with threshold current of only 300 mA have been obtained. The monitoring detector on the same InP substrate was confirmed to operate with high sensitivity, comparable with that of an external Ge photodiode.     

Characteristics of diffused-stripe InP/InGaAsP/InP lasers emitting around 1.55 µm

Fabrication and lasing characteristics of InGaAsP/InP lasers emitting around 1.55 μm are described. Zn-diffused stripe-geometry lasers with emission wavelengths in the1.53-1.60mum range were fabricated from InP/InGaAsP/InP DH epitaxial wafers prepared by a low temperature LPE technique. The dependence of the lasing charaeteristics on the stripe width was examined. The lowest threshold current (≃160 mA under CW operation at 27°C) was obtained for a laser with a 13 μm stripe. CW operation of the laser has been achieved at a heat-sink temperature as high as 53°C. For sufficiently narrow stripe widths (simeq6 mum), fundamental-transverse mode and single-longitudinal mode operation was obtained under CW operation. Moreover, the lasers have good high-frequency performance. The lasers showed excellent dynamic properties without waveform distortion under high-frequency (800 Mbits/s) large-signal pulse modulation. The full width at half maximum of the longitudinal mode envelope was approximately 30 Å at 800 Mbits/s.     

Low-threshold lasers fabricated by alignment-free impurity induceddisordering

An Si/SiN_x/Si trilayer diffusion source and mask is described and applied to an alignment-free process for fabricating lasers by impurity-induced disordering (IID). Edge-emitting lasers with continuous wave threshold currents of 4.8 mA were achieved, and folded-cavity surface-emitting lasers with Si disordered waveguides were demonstrated for the first time with a threshold of 11 mA. The process that makes possible self-aligned-metallization on a diffusion defined stripe will be useful in fabricating narrow stripe IID lasers and simplify processing for integration of IID waveguide devices     

A groove GaInAsP laser on semi-insulating InP using a laterally diffused junction

Low threshold current GaInAsP/InP groove lasers have been fabricated on semi-insulating InP substrates. Three n-type layers are grown with a single liquid phase epitaxial (LPE) growth process, and the p-n junction is formed by a lateral Zn diffusion. The active layer inside the groove provides a real index waveguide. Threshold currents as low as 14 mA with 300 μm cavity length are obtained. A single longitudinal mode at 1.3 μm up to1.4 I_{TH}is observed. The lasers operate with a single lateral mode when the active region width is less than 2.5 μm. This laser is suitable for monolithic integration with other optoelectronic devices.     

Low-threshold oxide stripe GaAs/GaAlAs lasers grown by MOCVD

MOCVD-grown insulator defined stripe GaAs/GaAlAs lasers with stripe widths of 6, 10, 20 and 150 ?m have been characterised. Uniform CW threshold currents as low as 45 mA, differential quantum efficiencies as high as 74%, and kink-free power levels as high as 20 mW/facet have been obtained in 160 ?m long, 6 ?m stripe lasers. The internal differential quantum efficiency measured from our 6 ?m stripe lasers approaches one. Single longitudinal mode operation of these lasers has also been observed.     

Low threshold planarized vertical-cavity surface-emitting lasers

Vertical-cavity surface-emitting lasers fabricated utilizing a self-aligned process to provide planarized contacts are discussed. A single 80-Å In_0.2Ga_0.8As strained quantum well was used in the active region. Emission was at 963 nm. Threshold currents under continuous-wave room temperature operation of 1.1 mA, at 4.0-V bias, were measured for numerous 12-μm×12-μm devices. Corresponding threshold current densities were 800 A/cm² (600 A/cm² for broad area devices). These are the lowest figures yet reported for this type of device. It was found that grading of the mirror had a marked effect on mirror resistance