Double Heterojunction Laser Research Articles

PbSnTe double-hetero junction laser diode and its application to mid-infrared spectroscopic imaging

Abstract In-doped n-PbTe/p-PbSnTe/Tl-doped p-PbTe LPE layers were successively grown for the fabrication of mid-infrared (λ∼7.5 μm) laser diodes (LDs) by using the constant temperature liquid phase epitaxy on (1 0 0) oriented p-type PbTe substrates. Substrate materials were prepared by the stoichiometry-controlled Bridgman method. Whereas, the present double hetero LDs have a simple broad contact structure, the threshold current density for lasing is as low as ∼200 A cm 2 . The emitted wavelength is tunable by changing the operation temperature. PbSnTe DH-LD was applied for the mid-infrared spectrum measurements of glycine and the spatial distribution imaging was obtained by using the specific absorption line (fingerprints), which vibration mode is originated from the skeleton oscillation of molecules. Another demonstration for the application of PbSnTe DH-LD spectrometer is the imaging of carrier distribution on Si wafers based on the change of free carrier absorption coefficients.

Line-shape study of water vapour by tunable diode laser spectrometer in the 822?832�nm wavelength region

A near-infrared tunable diode laser absorption spectrometer is set up to measure the air-induced broadening coefficients and the line-strength parameters of water-vapour overtone transitions within the (2,1,1)←(0,0,0) band in the 822–832 nm wavelength region. A Hitachi HL8311 E double hetero-junction structure diode laser is used as a probe. The diode laser controller is home-built and stable within ±10 μA and ±10 mK, respectively. The laser-head mount has a simple design and provides easy access whenever changing of the laser head is required. The diode laser emission wavelength is thermally tuned between 50 °C and 12 °C. Thermal tuning of the diode laser emission wavelength is used to reveal the mode structure of the diode laser and to probe the overtone-band transitions of water vapour within its operating wavelength range. Current tuning of the diode laser is used at a fixed laser temperature to study the transitions one at a time. A balanced detector is used to improve the S/N ratio of the spectrum. A phase sensitive detection technique is followed to obtain the first-derivative spectra of the overtone transitions. The first-derivative spectra have been recorded at different air pressures inside the sample cell while the water-vapour pressure is kept fixed. The first-derivative spectrum is numerically integrated to obtain the original line shape. The original line shape is fitted with a Voigt profile by using a nonlinear least-squares fit program to extract the air-broadening coefficient and the line-strength parameter. The data obtained in our work is compared with the results of the HITRAN database.

MID-INFRARED GaSb-BASED LASERS WITH TYPE-I HETEROINTERFACES

The design of room-temperature, InGaAsSb/AlGaAsSb diode lasers has evolved from the first double-heterojunction lasers described in 1980 that operated in the pulsed-current mode to present-day continuous–wave (CW), high-power, quantum–well diode lasers. We discuss in detail recent results from type-I-heterostructure, GaSb-based CW room-temperature diode lasers. The devices operate within the wavelength range of 1.8 to 2.7 μm, providing output powers up to several Watts. We analyze the factors limiting device performance.

GaSb–PbSe–GaSb double heterostructure midinfrared lasers

A GaSb/PbSe/GaSb double heterojunction laser structure is proposed. The advantages and feasibility of fabricating such lasers are discussed. Theoretical calculations show that the threshold gain for GaSb/PbSe lasers is much smaller than for traditional PbEuSe/PbSe lasers. Electrical confinement and heat dissipation is also significantly improved. The resulting much lower threshold currents and temperature difference between the active layer and heat sink should allow GaSb/PbSe lasers to operate in continuous wave mode above room temperature.

Molecular-beam epitaxial growth of GaxIn1−xP–GaAs (x∼0.5) double heterojunction laser diodes using solid phosphorus and arsenic valved cracking cells

Growth of GaxIn1−xP–GaAs (x∼0.5) double heterojunction injection lasers was achieved with molecular-beam epitaxy (MBE) employing phosphorus and arsenic valved cells. White phosphorus at 25 °C, generated in situ from amorphous red, provided the P4 vapor necessary for alloy growth. Photoluminescence performed on unintentionally doped epitaxial GaxIn1−xP (x=0.395–0.55) on GaAs showed 300 K spectral full-width-at-half-maximum between 35–40 meV and were as narrow as 9 meV at 77 K. Broad area (60×450 μm2) stripe geometry laser diodes with 0.1 μm active regions had threshold current densities on the order of 1.5 kA/cm2. Threshold current densities for diodes with 0.25 μm active region widths were about 2 kA/cm2. The data show optical devices and compounds grown by MBE with solid phosphorus and arsenic valved cracking cells are comparable to that realized by other techniques which use AsH3 and PH3 sources.

Numerical drift‐diffusion simulation of Auger hot electron transport in Ingaasp/Inp double heterojunction laser diodes

AbstractThis paper considers the adaptation of drift‐diffusion device simulation methodology to study Auger‐recombination‐induced hot electron transport characteristics in InGaAsP/InP double heterostructure laser diodes. In order to model the transport behaviour of the Auger hot electrons, we decompose the conventional electron current continuity equation into two components, with one for the Auger hot electrons and the other for the low‐energy electrons. These equations, which use the energy relaxation time parameter to model the dynamics of the Auger hot electrons, are then coupled with the hole current continuity equation and the Poisson equation to obtain self‐consistent solutions. Results from the case studies of one‐dimensional N‐p‐P InGaAsP/InP double heterojunction laser diodes with material composition corresponding to 1·3 μm and 1·55 μm wavelength emissions are presented. We have observed that hot electrons generated through Auger recombination inside the active region can spread into both the N‐ and the P‐InP cladding layers. Within the drift‐diffusion framework, it is demonstrated that the hot electron concentration in the N‐InP cladding layer can be five orders of magnitude higher than that in the P‐InP cladding layer. Because energy transport of the hot electrons in not modelled under the drift‐diffusion approximation, the simulated results are discussed to highlight some of the possible limitations in using drift‐diffusion physics to study Auger hot electron transport behaviour. The importance of taking energy transport into account is emphasized.

Chemical changes accompanying facet degradation of AlGaAs quantum well lasers

The temperature of single quantum well semiconductor laser facets increases during operation, eventually reaching a critical temperature, thermal runaway, and catastrophic optical damage. A study of changes in composition of the near-surface region of facets which accompany heating has been carried out for continuously operated, uncoated AlGaAs-GaAs-AlGaAs graded index separately confined heterostructure single quantum well lasers. High resolution depth profiles by scanning Auger microscopy show that the laser facets can be quite variable in initial composition, and undergo pronounced stoichiometry changes even during the first few minutes of operation. At longer times a continuing out-migration of the group III elements is observed. Unlike the double heterojunction lasers, facet oxidation is not pronounced and is not responsible for diffusion of Ga and Al. There are indications, however, that a slow leakage of oxygen into the crystal may occur. Spatially resolved analyses provide evidence that carrier-mediated elemental redistribution is an important factor in facet degradation. The progressive accumulation of defects which may act as non-radiative recombination centers provides a simple means of facet heating. Analyses of lasers which have suffered catastrophic damage indicate that the facets are not always melted, and that there is no typical chemical state which distinguishes them from facets of lasers which are fully operational. These results are compared to studies of facet degradation in double heterojunction lasers. Implications of the data for models of catastrophic optical damage are discussed.

Comparison of the facet heating behavior between AlGaAs single quantum-well lasers and double-heterojunction lasers

The facet heating behavior of AlGaAs double-heterojunction (DH) lasers was measured as a function of injection current using Raman microprobe spectroscopy. The result from the DH lasers is compared to AlGaAs ridge-waveguided single quantum-well (SQW) lasers. A clear discontinuity in the facet temperature rise was found below and above the lasing threshold for the DH lasers, indicating a substantial contribution to facet heating by the photon flux. This is in contrast to the facet heating behavior of SQW lasers in which photon flux has been shown to play only a minor role. The data suggest a large difference in the facet absorption of the lasing photons between the two types of lasers. This is further supported by the effect of argon laser probe beam induced facet heating on the diode laser’s output power.

High frequency modulation of light output power in double-heterojunction laser

High frequency modulation of light output power in double-heterojunction laser

Focused ion beam machining of mirror facets of a monolithically integrated GaAs/GaAlAs double heterojunction (DH) laser and its optical waveguide.

A specially designed coupled SEM/FIB system was used to realize high quality mirror facets in different laser structures. The dynamics of the ion milling were recorded and the geometrical effects of the ion bombardment were studied to optimize the working parameters. The light output characteristics of the GaAs and InP lasers obtained were measured. The optimized machining process was successfully applied to the realization of a monolithically integrated double heterostructure laser butt-coupled to its optical waveguide.

On the origin of the carrier leakage in GaInAsP/InP double-heterojunction lasers

The measured 950-nm emissions induced by carrier leakage are compared with theoretically calculated Auger-recombination-induced carrier leakage in GaInAsP/InP double-heterojunction lasers. The agreement obtained between measured and calculated results provides strong evidence that carrier leakage in these devices is related to the Auger-recombination processes.

Nonlinear characterization of modal gain and effective index saturation in channeled-substrate-planar double-heterojunction lasers

The nonlinear modal gain and effective index in AlGaAs/GaAs channel-substrate-planar double-heterojunction (CSP-DH) lasers are calculated as a function of the drive current and intracavity power. These functions are first computed using a self-consistent procedure that ties together the optical fields and the carrier distribution in the active layer. The functions are then suitably fit to a new empirical analytic expression that is useful for modeling the laser as a single device or as multiple lasers that are coherently locked. The specific analytic expressions are simple algebraic formulas that have six parameters that can be calculated using regression techniques. These parameters are computed for the CSP-DH laser as a function of the stripe contact width.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

CATHODOLUMINESCENCE IN DOUBLE HETEROJUNCTION LASERS

The cathodoluminescence mode of the Scanning Electron Microscope is used to evaluate local properties of the active layer of double-heterojunction lasers. The analysis of the Cathodoluminescence line-scans and spectra from cleaved laser surfaces, as a function of the external bias and of the incident beam current, give information about the interface quality, the internal efficiency and the local gain of stimulated emission. In order to make a quantitative interpretation of our experimental measurements, an analytical form of the tridimensional generation function, derived from a Monte-Carlo trajectory simulation, is used.

X-Ray Interference Measurements of Ultrathin Semiconductor Layers

AbstractWe present various x-ray diffraction phenomena from semiconductor hetero-epitaxial layers. Each of these phenomena gives useful information on the layers. Knowing what to look for in the x-ray rocking curve (XRC) can make this nondestructive technique a very powerful tool for characterization of a few A-several g.tm thick layers We discuss the use of individual Bragg peak, diffraction fringe, and interference structure to obtain layer information. We particularly emphasize the use of x-ray interference in studying buried strained quantum well or quantum barrier layers. We present experimental rocking curves of an AlGaAs/GaAs double heterojunction laser structure and GaInAs/GaAs strained layer superlattices in both &lt;001&gt; and &lt;111&gt; orientations.

New III-V double-heterojunction laser emitting near 3.2μm

Double heterostructure lasers based on the InAsSbP/InAsSb system have been prepared by liquid phase epitaxy. They operate at 78 K near 3.2 mu m, with a threshold current density of 4.5 kA/cm/sup 2/ in pulsed conditions. The characteristic temperature T/sub 0/ is 30 K. >

A theoretical analysis of Auger recombination induced energetic carrier leakage in GaInAsP/InP double heterojunction lasers and light emitting diodes

An Auger recombination induced energetic carrier leakage model is presented, which takes into consideration the rate of generation of energetic carriers through Auger recombination processes, the rate of energy relaxation of the energetic carriers through carrier-phonon interactions, and the leakage of energetic carriers over the heterojunction barriers limited by diffusion and drift mechanisms. By including this energetic carrier leakage in the rate equations of injected carriers, the leakage behavior of GaInAsP/InP double heterojunction lasers and light emitting diodes can be calculated. Analytic results are found to be in excellent agreement with experimental measurements.

ZnSe-ZnSxSe1−x and ZnSe-Zn1−xMnxSe metal-insulator-semiconductor heterostructure lasers

Metal-insulator-semiconductors (MIS) heterostructures, using ZnSe and ZnSe-based ternary compounds such as ZnSSe and ZnMnSe, have been proposed to obtain efficient blue light emission and lasing action. MIS laser structures are particularly desirable for wide energy gap semiconductors in which the controlled doping of n- and p-type impurities is somewhat difficult to realize. The MIS heterostructure laser is a novel device as an alternative to the conventional p-n double heterojunction laser. In these lasers, efficient minority carrier injection in the active layer is achieved from the MIS interface in place of a p-n heterojunstion emitter. Emitted photons are confined in the active layer as they are reflected by a heterostructure dielectric discontinuity (e.g., ZnSe-ZnSxSe1-x) on one side and the perfectly reflecting surface of the barrier metal on the other. Modal analysis of a stripe geometry Au-SiO2-n-ZnSe-n-ZnSxSe1-x-n-ZnSe MIS laser is presented. The output characteristics are compared with a conventional p-n double heterostructure laser. A MIS heterostructure to realize a distributed feedback laser is also discussed.

Crystal growth of GaAs and AlGaAs by OMVPE using triethylarsenic as arsenic source

Triethylarsenic (TEAs), which is much less toxic than arsine, was used as an arsenic source for organometallic vapor-phase epitaxy (OMVPE) of GaAs and AlGaAs. The lower growth rates of GaAs at higher growth temperatures were remarkably increased by a low pressure growth. AlGaAs with a mirror-like smooth surface was obtained for the first time over a wide range of growth temperatures 600–710°C, V/III ratios 3–10, and Al compositions 0—0.5. Purity of TEAs was found to be an important key for good quality AlGaAs epilayers. The growth rate of AlGaAs became lower and the Al composition higher, as the growth temperature was increased. Room temperature, pulsed operation of double heterojunction laser diodes, which were fabricated with the grown layers of GaAs and AlGaAs doped with Si or Zn, was achieved at the first trial.

Analysis and observation of current spreading and current concentrating effects in constricted double-heterojunction lasers

Current spreading and current concentrating effects of constricted double-heterojunction lasers (CDH) have been studied. A quantitative formula of the current profile for CDH structure has been obtained theoretically and verified experimentally. In addition, we have compared the influence of these two effects on the threshold current of CDH lasers. From this study, we proposed a scheme to reduce threshold current and fabricated lasers with typical threshold currents of 30–50 mA. The lowest threshold current is 27.5 mA (L=125 μm, s=10 μm, 21 °C, cw). Our results also indicated that the temperature coefficient T0 of CDH lasers will be improved only through increasing side leakage current.

Self-consistent analysis of gain saturation in channeled-substrate-planar double-heterojunction lasers

A self-consistent model for semiconductor lasers [using the channeled-substrate-planar (CSP) double-heterojunction (DH) laser as an example] which does not assume constant optical power along the laser axis is developed. This approach allows for the analysis of high-power lasers with low facet reflectivities which produce nonuniform photon densities along the propagation direction. Analytical equations for the modal gain coefficient, the threshold current density, and the radiated power for a specific CSP laser structure are obtained.