Stripe Contact Research Articles

Electromigration behaviour of SiO 2-covered, large-grained, narrow AlSi lines with ohmic contacts

Starting from large-grained, narrow AlSi-lines which were characterized by homogeneous bulk mass flow unde rstress conditions, electromigration tests were performed with 8 × 10 5 A/cm 2 at 200°C, using an additional SiO 2 passivation layer. The covering film drastically degraded electromigration behaviour. Premature failures were produced by contact openings, increased contact resistances and stripe interruptions. On the one hand, the covering films increased the Al drift velocity substantially. On the other hand, AlSi-compounds or Si-nodules were formed, which favoured void growth and stripe interruptions. Those interruptions even occurred if the net Al mass flow seemed to be negligible. When Si was omitted, failure times increased considerably.

Analytical solution for the lateral current distribution in multiple stripe laser diodes

The lateral profile of the injection current along the active layer in multiple stripe laser diodes is analyzed for the practical case of homogeneous current density within each individual stripe contact. By means of conformal mapping an exact analytical solution is found for arbitrary contact configurations (number, width, and location) driven with different currents. The simple form of the solution eases the analysis of modal gain and supermode discrimination in gain-guided and index-guided arrays of stripe-geometry laser diodes.

Emission wavelength of AlGaAs-GaAs multiple quantum well lasers

We have recorded spontaneous emission spectra from multiple quantum well lasers grown by molecular beam epitaxy with 25-Å-wide GaAs wells by opening a window in the top contact stripe. These spectra have a low-energy tail and consequently the gain spectra derived from them show that laser emission occurs at a lower photon energy than the lowest energy confined particle transition. The observed laser wavelength and threshold current are consistent with the position of the peak in the gain spectrum.

Comparison of current spreading in stripe contact semiconductor lasers

The current profile at the active layer of an oxide stripe semiconductor laser is compared with those where there is an additional current channelling layer. For 3 µm and 10 µm stripe widths, it is found that a current channelling layer of 1 µm thick marginally improves the current within the stripe width by between 2% to 6%, but, more importantly, it eliminates the dip in the current profile at the centre of the stripe for the larger stripe width. For much larger stripe widths, such as at 20 µm, the current channelling layer needs to be correspondingly thicker to be effective in removing the dip in the current profile at the centre of the stripe.

Investigation of mechanisms of multimode emission from double-heterostructure AlGaAs injection lasers with narrow stripe contacts

An investigation was made of the spectral characteristics of planar stripe (contact width 6--8 ..mu..) lasers made of AlGaAs heterostructures. The steady-state emission spectrum could be of multimode type because of the high level of spontaneous emission in the lasing mode. The spectrum then became narrower on increase in the power and in the limit changed to the single-mode form. However, in the presence of self-modulation processes the multimode nature of the emission spectrum could be explained by a theory of transient effects and in this case the width of the spectrum increased on increase in the power.

Single contact tailored gain phased array of semiconductor lasers

We demonstrate a single contact tailored gain-guided array in which the gain profile across the array is made strongly asymmetric by varying the width of the contact stripes. A proton isolated array of six (GaAl)As lasers with 5-μm separations and widths varying linearly between 3 and 8 μm had a single lobed far field 2° wide, close to the diffraction limit for a single supermode. Fabrication of this device is simple, and suited to large-scale processing techniques. We also show that in such an asymmetric gain-guided array the fundamental mode is favored over higher order modes, and that higher order modes can have single lobed far-field patterns differing only slightly from that of the fundamental.

Influence of photon transport on diffusion processes in stripe heterolasers

The influence of photon transport on the diffusion of nonequilibrium charge carriers in heterolasers with stripe contact and in structures with a transverse p-n junction arrangement is taken into account. Results are presented of a machine computation of the nonequilibrium charge carrier (NCC) concentration profile and the radiation density in the active layer of AlGaAs lasers in the prethreshold pumping mode.

Cw room-temperature operation of GaAlAs single quantum well visible (7300 Å) diode lasers at 100 mW

100-mW room-temperature cw laser operation at 7300 Å has been achieved in a Ga1−xAlxAs (x∼0.22), ∼300 Å thick, single quantum well double heterostructure diode grown by organometallic vapor phase epitaxy. The proton-delineated stripe contact is 6 μm wide, and the front and rear laser facets are coated for antireflection and high reflection respectively. The cw threshold current is 86 mA for a 250-μm-long device, and linear output power versus current characteristics are observed up to 100 mW with an external differential quantum efficiency of 1 W/A (59%). cw output power exceeds 13 mW at 100 °C. Between 25–55 °C, the pulsed threshold current varies exponentially with temperature T as exp(T/T0), where T0∼187 K.

Effect of longitudinal variations in current injection and carrier concentration in laser diodes

The effects of nonuniform current injection along the length of a semiconductor laser are investigated using multiple segmented stripe contact lasers. The results of the experiments are analyzed with a model for which the carrier concentration, gain, and photon density are functions of position. From the model, it was determined that nonuniform current injection caused large variations in the optical field within the laser, and the field produced a redistribution of electrical carriers in the active region. The nonlinearities in the light versus current measurements were explained by the redistribution of carriers as the optical field changed.

Modal Solutions of Active Dielectric Waveguides by Approximate Methods

Approximate methods are used to obtain the modal properties of stripe-contact semiconductor injection lasers using a planar three-layer waveguide model. The central active layer has a dielectric constant that varies smoothly along the direction parallel to the heterojunction boundaries. The complex dielectric constant under the stripe contact is dependent on the gain and approaches a constant value at large lateral distances. The two methods are compared in terms of their modal propagation constants. An application of the effective index method facilitates a physical understanding of dielectric waveguide modes as well as providing an efficient calculation procedure.

An Analytical Solution of the Lateral Current Spreading and Diffusion Problem in Narrow Oxide Stripe (GaAl)As/GaAs DH Lasers

An exact solution is presented to the problem of lateral current spreading in the resistive layer of oxide stripe geometry DH lasers. The two-dimensional Laplace equation was solved by conformal mapping using the Schwarz-Christoffel transformation. The diffusion equation containing nonlinear recombination terms was solved numerically. Computed examples demonstrate that the customary one-dimensioned treatment of the resistive layer or the assumption of constant current density under the stripe contact are not always justified, particularly for narrow stripe widths and low specific resistivities. This region of low values of the resistivity and stripe width, however, is of great practical interest in the design of oxide stripe lasers having high thermal stability and kink-free characteristics.

An analytical solution of the lateral current spreading and diffusion problem in narrow oxide stripe (GaAl)As/GaAs DH lasers

An exact solution is presented to the problem of lateral current spreading in the resistive layer of oxide stripe geometry DH lasers. The two-dimensional Laplace equation was solved by conformal mapping using the Schwarz-Christoffel transformation. The diffusion equation containing nonlinear recombination terms was solved numerically. Computed examples demonstrate that the customary one-dimensional treatment of the resistive layer or the assumption of constant current density under the stripe contact are not always justified, particularly for narrow stripe widths and low specific resistivities. This region of low values of the resistivity and stripe width, however, is of great practical interest in the design of oxide stripe lasers having high thermal stability and kink-free characteristics.

Monolithic integration of InGaAsP heterostructure lasers and electrooptical devices

Monolithically integrated InGaAsP heterostructure lasers ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda = 1.3 \mu</tex> m) coupled to low-loss InGaAsP waveguides are described. The integrated InGaAsP etched-mirror lasers are fabricated using liquid-phase epitaxy and a new material-selective chemical etching technique. The integrated devices have been operated as optically coupled lasers, photodiodes, and resonant optical amplifiers. For lasers with two etched mirrors, differential transfer efficiencies as high as 8 percent have been measured for waveguide-coupled laser-photodiode pairs. The waveguide-coupled InGaAsP lasers with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12.5 \times 300 \mu</tex> m contact stripes and two etched mirrors have room-temperature threshold currents as low as 580 mA pulsed. Similarly fabricated etched-mirror lasers without the waveguide layer have threshold currents as low as 280 mA pulsed (25 μm stripewidth). In order to obtain lower threshold currents and stable transverse-mode characteristics, InGaAsP buried-heterostructure (BH) lasers with chemically etched mirrors have been fabricated. The etched-mirror BH lasers have threshold currents as low as 160 mA pulsed. Evaluation of the etched-mirror reflectivity for the material-selective-etched lasers yielded an estimated reflectivity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R = 0.01-0.03</tex> and scattering loss <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S = 0.6-0.8</tex> . Similar evaluation of a BH laser with non-material-selective-etched mirrors gave an estimated reflectivity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R = 0.11</tex> and scattering loss <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S = 0.4</tex> . Analysis of the mode reflectivity of nonideal double-heterostructure laser mirrors shows that the reflectivity is limited by misalignment (tilt) of the etched mirrors.

Theoretical analysis of current spreading in stripe-geometry injection lasers

Iterative techniques have been used to solve the current spreading problem in stripe contact injection lasers. The effects of n- and p-passive layers, contact resistance, and carrier diffusion in the active layer are considered. The results are presented in normalised form, facilitating their use in device design.

AlGaAs/GaAs microcleaved facet (MCF) laser monolithically integrated with photodiode

A new AlGaAs/GaAs double-heterostructure laser with microcleaved facets, restricted just at stripe contact edges, has been developed. This laser and a junction photodiode have been monolithically integrated in a single GaAs substrate. Low-threshold current lasing and high-fidelity monitoring characteristics have been demonstrated.

Stripe-geometry laser with in-situ ohmic contact and self-aligned native surface oxide mask for current isolation prepared by molecular beam epitaxy

A simple stripe-geometry laser is prepared by molecular beam epitaxy with an in-situ ohmic contact stripe and self-aligned native surface oxide mask for current isolation. The thresholds are about 70 mA for 5 μm-wide and 380 μm-long stripes. The light/current characteristics are linear up to ̃8–10 mW/mirror with a spontaneous emission level at threshold of ̃0.3 mW/mirror. The temperature coefficient T0 measured for one wafer is as high as 255 K.

A Schottky-barrier-delineated stripe structure for a GaInAsP-InP cw Laser

A new stripe geometry for cw GaInAsP-InP layers is presented. The laser consists of a stripe contact defined on the In0.53 Ga0.47 As cap layer of a conventional double heterostructure. It is surrounded by two lateral-reverse-biased Schottky diodes fabricated onto the p-type confinement layer. These lasers have a threshold curent of 100 mA for 320-μm-long and 20-μm-wide stripes and operate in the zero-order transverse mode.

Channeled substrate nonplanar laser analysis - Part I: Formulation and the plano-convex waveguide laser

An analysis of diode lasers with lateral thickness variations in the active and/or guiding layers is presented. The technique, which applies both at and above threshold, models the current flow from the stripe contact, the charge diffusion within the active region, the modal wave propagation, and the cavity condition, self-consistently, such that the phenomena of spatial hole burning in the charge distribution by the modal intensity and the changes in the complex refractive index produced by the charges are accounted for simultaneously. Results are obtained for threshold current as well as laser behavior above threshold, including the charge density distribution, the mode patterns, the differential quantum efficiency, and the lowest order mode power at which the laser begins oscillating in more than one spatial transverse mode. A study of the piano-convex waveguide laser is described in detail and an Appendix discussing the mathematical methods is included.

Double-heterojunction laser diodes with multiply segmented contacts

Multiple segment stripe contact (MSSC) diode lasers, in which the pumping current density, and thus the gain or loss, can be varied and controlled along the length of the laser stripe, are reported. For different combinations and magnitudes of current density into the eight segments, self-pulsing, optical switching, bistability, hysteresis, and extremely high external differential quantum efficiencies can each be achieved. By simultaneously monitoring the voltage on the individual segments, changes in the carrier concentration and thereby changes in the gain and loss as a function of optical density and position along the stripe have also been observed. The use of MSSC lasers in the study of basic laser diode properties as well as novel devices of interest in their own right is suggested.

Calculation of lateral current spreading and series resistance effects in oxide stripe geometry GaAs-GaAlAs DH lasers

An exact solution is presented to the problem of current spreading in the resistive layer of stripe geometry DH lasers. Computed examples demonstrate that the customary one-dimensional treatment of the resistive layer or the assumption of constant current density distribution under the stripe contact are not always justified.