Transverse Junction Stripe Laser Research Articles

Transverse-junction-stripe GaAs-AlGaAs lasers for squeezed light generation

We fabricated 850-nm GaAs transverse-junction-stripe (TJS) lasers by an improved metal-organic chemical vapor deposition (MOCVD) and double Zn diffusion process. The high V/III ratio used during the MOCVD growth significantly reduced the intermixing of GaAs active layer and AlGaAs cladding layers. The modified process realized good confinement for both carriers and photons and smaller saturable loss. We measured squeezing of -2.8 dB (-4.5 dB after correction for detection efficiency) at a pumping rate of I/I/sub th//spl ap/20 from these lasers, which is in close agreement with the theoretical limit. This squeezing remained unchanged under injection locking, indicating almost perfect conservation of the intensity noise correlation among the longitudinal modes. These TJS lasers had very small low-frequency 1/f noise.

Unique top-driven low-threshold lasers by impurity-induced disordering

Top-driven lasers have been fabricated by impurity-induced disordering (IID). Compared with conventional top-driven lasers, that is, transverse-junction-stripe (TJS) lasers, the top-driven IID (TID) lasers are unique in that the carriers in the active quantum-well stripe, are injected vertically from (instead of laterally between) the cladding layers of the lasers. Because vertical injection is much more efficient than lateral injection, the threshold current of the TID lasers is lower than that of TJS lasers by a factor of 2-10. The lowest threshold current observed for the TID lasers was 1.6 mA under room-temperature continuous-wave (CW) operation. By using proper material design and device processing, the top n-type contact of the TID lasers obtained is virtually as good as the bottom n-type contact of conventional IID lasers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GaAs/AlGaAs double-heterojunction lateral p-i-n ridge waveguide laser

A new type of double-heterojunction lateral current injection GaAs/AIGaAs <i>p-i-n</i> ridge waveguide laser is described. The device employs intrinsic materials in the active region to reduce the parasites in the laser, thereby lowering the required threshold current and increasing the quantum efficiency of the device. The use of ridge waveguide structure provides better optical confinement than the conventional lateral injection lasers and avoids the regrowth required for buried heterostructure transverse junction stripe (TJS) lasers. Two-dimensional self-consistent simulations have been carried out, using our finite-element light emitter simulator (FELES), for the purpose of proof of concept and evaluation of the device operation and performance. The results show that the device has a low threshold current, a good differential efficiency, a low capacitance (0.028 pF at zero bias), and a low dynamic resistance (< 2.3 Ω).

AlGaAs diode laser blue shift resulting from fast neutron irradiation

Six TJS (transverse junction stripe) AlGaAs diode lasers were exposed to fast neutrons with fluences ranging from 2×1012 to 3×1013 n/cm2, and their tuning, gain, and dispersion curves were measured. The tuning and gain curves of four lasers showed blue shifts of several meV at neutron fluences as low as 2×1012 n/cm2; the other two lasers never showed this blue shift. In addition, the lasers that displayed a blue shift also showed an increase in their threshold currents. None of the lasers exhibited any change in their dispersion curves. To explain the blue shift, it is hypothesized that neutron irradiation reduces the efficiency for lasing in the bandtail states of these devices, forcing lasing action to occur between states with greater energy separation. A model in which the reduced efficiency takes the form of a decrease in the transition matrix element is found to yield blue shifts of the correct order of magnitude. Though bandtail effects may also explain the difference in radiation sensitivity among the TJS lasers, at present the reason why only four of the six lasers blue shifted after neutron irradiation is not well understood.

Room-temperature continuous wave operation of a visible AlGaAs/InGaP transverse junction stripe laser grown by liquid phase epitaxy

Continuous wave operation of an AlGaAs/InGaP/AlGaAs transverse junction stripe (TJS) laser diode (LD) has been achieved at room temperature for the first time. It was grown on a (100) GaAs semi-insulating (SI) substrate by liquid phase epitaxy (LPE). This device, with 100-μm-wide and 500-μm long Zn diffused stripe geometry, exhibits a room-temperature threshold current of 420 mA. The corresponding threshold current density is as low as 0.85 kA/cm2, which is the lowest value for those electroluminescent devices with an AlGaAs/InGaP/AlGaAs heterostructure. An emission peak wavelength of 615 nm and a light output power of 300 μW/facet were also reported.

Surface and bulk leakage currents in transverse junction stripe lasers

This paper presents two ways to reduce leakage currents in transverse junction stripe (TJS) lasers: by reducing surface leakage current and by reducing bulk leakage current. The surface leakage is reduced by treatment with (NH4)2S, while the bulk leakage current is reduced by isoelectronic doping with indium. We report the first detailed experimental investigation on the effect of the chemical treatments on the electrical characteristics and laser thresholds of TJS lasers. Surface treatments of (NH4)2S are demonstrated that reduce surface leakage currents in current injection lasers. After the chemical treatments, a 20-fold reduction in current has been achieved with GaAs/AlGaAs lattice-matched multiple-quantum-well TJS lasers. The laser thresholds of lattice-matched TJS lasers are reduced by 12 mA (or 16%) after the chemical treatments. In addition, InGaAs-GaAs-AlGaAs strained-layer single-quantum-well lasers are treated chemically and a reduction in the laser threshold (10 mA or 14%) is observed. The surface treatments are still effective after 7 days. We also report the first experimental investigation on the effect of isoelectronic In doping on the current-voltage characteristics of Zn-diffused lateral p-n junctions. The trap density in an In-doped AlGaAs layer is reduced by more than one order of magnitude compared to that in an AlGaAs layer without In doping. Bulk leakage currents (shunting currents) in TJS lasers can be reduced by using isoelectronic In doping, which should reduce threshold currents and improve the temperature dependence of TJS lasers.

Picosecond optical detection of longitudinal spatial hole burning in an AlGaAs semiconductor laser

Summary form only given. The author reports the observation of spatially and temporally resolved carrier dynamics in the cavity of a top-surface AlGaAs laser using a modified picosecond differential phase-contrast confocal microscope, which has a single optical probe spot. The sample in the experiment was an AlGaAs crank transverse junction stripe laser. It was prebiased below threshold, and a 2-mA, 100-MHz sine wave signal was used to modulate the charge density within the cavity. The optical probe beam was focused onto the top of the AlGaAs laser sample and x-y scanned across its surface. The measurements show uniform charge density along the edges of the laser cavity and longitudinal spatial hole burning along the laser cavity center. The temporal variation of carriers within the laser cavity was also observed by focusing the picosecond 1.3- mu m laser probing spot to the center of the device. The measurements demonstrate that the internal charge level overshoots and then clamps at the threshold level, where the amount of overshoot is proportional to the overdrive current. >

Folded-cavity transverse junction stripe surface-emitting laser

A novel surface-emitting laser with a transverse junction stripe (TJS) and a folded-cavity configuration, which has an internal 45° mirror facet to direct the light normal to the surface, has been achieved for the first time. The fabrication of the 45° mirror facet was carried out using a simple angled reactive ion etching technique, and the laser performance yielded a threshold current of 31 mA and an external differential quantum efficiency of 24% per facet, which are comparable to those of conventional TJS lasers.

Operating characteristics and elevated temperature lifetests of focused ion beam micromachined transverse junction stripe lasers

The operating characteristics of transverse junction stripe diode lasers with focused ion beam micromachined mirrors are shown to be comparable to those with cleaved facet mirrors. Stable cw operation for more than 2200 h was observed in an aging test at 55 °C.

ALGAAS/GAAS TJS laser diodes fabricated on Si substrates by MOCVD

AlGaAs/GaAs TJS (Transverse Junction Stripe) laser diodes are fabricated on p-Si substrates by MOCVD. The preferential Zn diffusion is performed in DH structure on Si at 650°C using sputtered SiO 2 as diffusion mask. The diodes have lased at room temperature (27°C) pulsed conditions with the minimum threshold current of 379mA.

Strained layer and lattice matched transverse junction stripe quantum well lasers for continuous room temperature operation

Two new Transverse Junction Stripe (TJS) laser structures using lattice matched AlGaAsGaAs and strained layer InGaAsGaAsAlGaAs quantum wells have been demonstrated. The lasers are grown by molecular beam epitaxy and the junction is produced by a two step zinc diffusion and anneal. The diffusion process produces a lateral heterojunction (in addition to the as grown heterojunctions) by diffusion enhanced compositional disordering of the quantum well active region. Both lasers exhibit low thresholds (20–30 mA, continuous wave, room temperature) and single mode operation. The excellent performance of both lasers indicates that high quality lateral +-p-n junctions and heterojunctions can be formed by zinc diffusion enhanced compositional disordering of both lattice matched GaAsAlGaAs and strained layer InGaAsGaAsAlGaAs quantum well structures. The threshold current versus temperature, emission wavelength versus annealing time and preliminary lifetime data are presented.

New low capacitance transverse junction stripe AlGaAs/GaAs laser for planar laser-MESFET integration

A transverse junction stripe laser structure with a very low parasitic capacitance, compatible with an entirely planar laser-MESFET integration, is presented. The laser, obtained by two successive n (S) and p (Zn) diffusions across undoped AlGaAs/GaAs double heterostructure layers, has a threshold current of Ith = 55 mA. A very low parasitic capacitance Cs = 0.6 pF is measured, with a corresponding rolloff time constant of tr = 9 ps.

Nonselective etching of GaAs/AlGaAs double heterostructure laser facets by Cl2 reactive ion etching in a load-locked system

Reactive ion etching was used for etching laser facets of GaAs/AlGaAs transverse junction stripe lasers. A new load-locked reactive ion etching system was developed to dramatically reduce the background partial pressure of O2 and H2O in the chamber, substantially reducing the oxidation of AlGaAs and permitting equal rate etching of GaAs and AlGaAs with smooth vertical facets. Etching is performed with a chlorine plasma at a low pressure (0.5 mTorr), and bias voltage (−350 V) at a rate of ∼850 Å/min. This simple, single-step dry etching process is suitable for optoelectronic integration and eliminates the requirement of unreliable wet chemical etching or microcleaving techniques. This new system is used to fabricate transverse junction stripe lasers with facet reflectivities of more than 16%. These high quality dry etched facets result in only a 7.5% increase of the threshold current above that of lasers with cleaved facets.

Continuous room-temperature operation of an InGaAs-GaAs-AlGaAs strained-layer laser

We report the first continuous wave room-temperature InGaAs-GaAs-AlGaAs strained-layer semiconductor laser diode grown by molecular beam epitaxy. The laser is a multiple quantum well transverse junction stripe laser with a lateral heterojunction fabricated by zinc diffusion enhanced compositional disordering. The low-threshold (20 mA) and single-mode performance of the laser demonstrates that a high-quality lateral p+-p-n junction and lateral heterobarrier can be formed by zinc diffusion compositional disordering of a strained-layer InGaAs-GaAs-AlGaAs quantum well heterostructure.

GaAs/AlGaAs distributed feedback transverse junction stripe laser grown by molecular beam epitaxy

GaAs/AlGaAs transverse junction stripe lasers with a distributed feedback structure were fabricated. The cw threshold current was 27 mA at 20 °C. The laser operated in a pure single longitudinal mode at the wavelength of 867 nm.

AlGaAs/GaAs transverse junction stripe lasers fabricated on Si substrates using superlattice intermediate layers by MOCVD

TJS lasers are fabricated on Si substrates by diffusing Zn using sputtered SiO 2 as a mask, and the lasing properties are measured. The minimum threshold current of 379 mA and a differential efficiency of 2.2 percent have been obtained. The detailed fabrication procedure and laser characteristics are described in this paper.

Buried transverse-junction stripe laser for optoelectronic-integrated circuits

A buried transverse-junction stripe (TJS) laser, a suitable laser diode for integration, has been fabricated using molecular-beam epitaxial growth. The fundamental characteristics of the laser were as good as those of a conventional TJS laser. We have also demonstrated a fabrication process for the laser that is compatible with that for metal-semiconductor field-effect transistors (MESFETs) to be monolithically integrated. The characteristics of the MESFETs fabricated on substrates processed for the laser were the same as those fabricated on virgin substrates when such processed substrates were etched 2 μm deep.

Monolithic integration of a transverse-junction stripe laser and metal-semiconductor field-effect transistors on a semi-insulating GaAs substrate

A buried transverse-junction stripe laser diode and two metal-semiconductor field-effect transistors were monolithically integrated using two-step molecular beam epitaxy. This device had an almost flat surface well suited for the integration. High performance and high-speed operation (<1GHz) have been demonstrated in this integrated device for the first time.

GaAlAs/GaAs TJS Lasers on Si Substrates Operating at Room Temperature Fabricated by MOCVD

GaAlAs/GaAs TJS (transverse junction stripe) laser diodes were fabricated on p-Si substrates using strained super lattice intermediate layers. The diodes have lased at room temperature (27°C) pulsed conditions. The lowest threshold current is 379 mA.

VIA-8 transverse junction stripe laser with a lateral heterobarrier by diffusion-enhanced disordering

VIA-8 transverse junction stripe laser with a lateral heterobarrier by diffusion-enhanced disordering