Active Region Width Research Articles

Performance of a new ohmic contact for GaAs particle detectors

In recent papers, we have investigated, within the context of the RD-8 experiment, the behaviour as a function of bias of the active region of particle detectors made by Alenia SpA on semi-insulating liquid encapsulated Czochralski gallium arsenide: the active region width depends linearly on the bias voltage. The diodes were found to break down as soon as the field reached the back ohmic contact. This suggested that the ohmic contact was injecting holes into the diode, therefore we have decided to develop a new, non-injecting, non-alloyed ohmic contact. This new contact allows us to go far beyond, five times, the voltage bias necessary to have a fully active detector. The higher voltage reached by the detectors helps us improve the charge collection efficiency, up to more than 95% for alphas and more than 90% for beta (mips) particles and X-rays, giving a more stable operation of the detectors. For the first time we can explore the characteristics of a GaAs detector beyond the voltage needed for it to be completely active.

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.

An optical-beam-induced-current study of active region and charge collection efficiency of GaAs particle detectors

In a recent paper, it was described how semi-insulating (SI) liquid encapsulated Czochralski (LEC) gallium arsenide particle detectors made by Alenia SpA have been tested and found to be understandable in terms of one function: the local charge collection efficiency. We have now measured, always within the context of the RD8 experiment, the local charge collection efficiency for these diodes using a technique called OBIC (optical beam induced current) and derived the active region width ( W) as a function of bias in a range of values lower than those obtainable with particles. Using data both from OBIC and from the previous paper, W is found to behave approximately linearly as a function of bias larger than about 50 V. Below this value, W follows a square root law as a function of bias.

Linear sensitivity analysis of coupled arrays of lasers under random active-region width variations

An analytical and numerical study of the sensitivity of a one-dimensional evanescently coupled array of real index-guided (no antiguiding) semiconductor lasers under random device width variation is carried out with the aim of characterizing the far-field disturbance as a function of the variance of d (device active width), the number of devices n, and the interelement coupling κ. It is shown that the sensitivity of the far-field amplitude distribution increases approximately linearly with n up to n ≃ 20 with a given κ. A simple expression is derived that relates the maximum allowable variance of device widths for a given n under the constraint of nondegeneracy of the lowest-order eigenvalues. The size of an array that may be expected to remain in the fundamental mode under given perturbations is deduced. It is predicted that if this value is exceeded the array will break up into domains of in-phase regions separated by π rad in phase, and a formula is derived that gives the size of such domains.

Computational modeling of nanostructured porous silicon

Abstract The finite diffusion length model generates patterns which are similar to the nanostructural features in porous silicon formed by electrochemical anodizing. The simulated patterns have a nearly constant density away from the interface regions. The variation of number of particles with distance is linear on a double log plot, in the regions away from interfaces. We report that the estimation of the width of the active region between the porous and the bulk lattice can be made by observing the transition from a region of constant slope to a region of zero slope on the log-log plot of number of aggregating particles versus distance.

Submilliampere threshold buried-heterostructure InGaAs/GaAs single quantum well lasers grown by selective-area epitaxy

Strained-layer InGaAs-GaAs-AlGaAs single quantum well buried heterostructure lasers grown by selective-area MOCVD are described. Threshold currents of 2.65 mA for an uncoated device and 0.97 mA for a coated device have been obtained. A peak optical output power of 170 mW per uncoated facet for a device with a 4 /spl mu/m active region width was also achieved. Peak emissions wavelengths range from 0.956 to 1.032 /spl mu/m. >

Finite-element thermal model for buried-heterostructure diode lasers

First results of our new finite-element modelling of thermal properties of GaAs/(AlGa)As buried-heterostructure (BH) lasers are reported. The calculus procedure is very efficient, so we have used a standard IBM PC/XT microcomputer. For the stripe active-region width of 1 μm, the thermal resistance of the laser was determined to be about 70 KW-1, whereas its electrical resistance was about 6 ohms. To the best of our knowledge, isothermal lines within BH lasers have been obtained for the first time. The isothermal configuration enables us to analyse heat-spreading phenomena in BH lasers, which makes possible thermal optimization of the laser construction.

Dynamic magnetization changes in laminated Permalloy films

Laminated soft magnetic films separated by nonmagnetic interlayers have edge-curling walls (ECWs) at the pattern edge. The authors have investigated dynamic magnetization changes near the ECW in strip-shaped laminated Permalloy films. Observation results obtained by scanning Kerr effect microscope at 10 MHz show the unique magnetization behavior-that is, inactive (weak Kerr signal) regions at the strip edges and magnetization change peaks inside the inactive regions. The edge region is observed as the inactive region under an excitation field smaller than the switching field in the ECW. According to the magnetization change calculation, the peak appears because the magnetization near the ECW shows a different behavior depending on the external field direction. Further examination shows that the ratio of the active region width in the actual strip width is changed by the layer configuration. >

AlGaAs/GaAs buried quantum well laser diodes by one time selective metalorganic chemical vapor deposition growth on dielectric window stripes

AlGaAs graded-index separate-confinement heterostructure lasers with lateral mode confinement are realized by one time metalorganic chemical vapor deposition with silicon dioxide stripes as selective masks and current blocking layers. The effect of the active region width on lasing characteristics is investigated. The threshold current and external quantum efficiency are around 12 mA and 70%, respectively, for narrow lasers. Elevated waveguide structure formed by the growth-rate difference between (100) and sidewall planes was effective for stable lateral mode characteristics.

High-power buried InGaAsP/GaAs (λ=0.8 μm) laser diodes

Buried InGaAsP/GaAs (λ=0.78 μm) separate confinement-single quantum well laser diodes have been prepared and studied for the first time. It has been shown that a stable far field pattern can be observed even at 500 mW continuous wave (cw) output power for diodes with active region width of about 7 μm, and single zero-mode operation has been obtained up to 170 mW cw for diodes with a width of 3.8 μm. Mirror facet overheating for the diodes studied was an order of magnitude less than that for similar AlGaAs/GaAs diodes.

Low threshold current 1.5- mu m buried heterostructure lasers using strained quaternary quantum wells

Buried heterostructure lasers operating at a wavelength of 1.5 mu m with four compressively strained quaternary quantum wells (strain approximately 1.8%, thickness approximately 90 AA) and current blocking layers were made using atmospheric pressure metalorganic chemical vapor deposition. Pulsed room-temperature threshold currents for uncoated devices as low as 4.1 mA and as low as 0.8 mA for devices with high reflectivity mirror coatings are reported. The dependence of threshold current on active region width is consistent with broad-area laser measurements. >

Active dielectric film laser

A laser configuration of an optical amplifier that consists of an active dielectric thin film is described. Both the spatial and the temporal mode structure are studied. Analytical and numerical formulations are used to describe the effects of this laser configuration, and experiments are performed to verify the predicted results. It is predicted and observed that the resonator beam width is dominated by the active region width of the film, not by the resonator-mirror curvature.

Gain of TE-TM modes in quantum-well lasers

Semiclassical laser theory is rigorously applied to semiconductor lasers in order to obtain both the complete TE and TM linear gain. The resulting expressions for the modal gain in heterostructure lasers differ in form from those conventionally accepted. In particular, the conventional modal gain written as the product of a confinement factor and a bulk gain is only an approximation of the true modal gain derived. The conventional expression relies on an explicit definition of the active region of the laser, which can be ambiguous when certain heterostructures, such as parabolic quantum wells, are to be treated. This ambiguity is eliminated by the gain expressions as a more natural active region defined by the product of electron and hole wave functions emerges. The relevant approximations which allow the newly derived gain equations to be written in forms similar to the conventional expressions for single quantum well, multiquantum well (MQW), and in wide active region lasers are explicitly shown. >

A new selective MOVPE regrowth process utilizing in-situ vapor phase etching for optoelectronic integrated circuits

Abstract We describe a new selective MOVPE regrowth technique combined with an in-situ vapor phase mesa-etching process and its application for the fabrication of transverse-junction buried hetero-structures. This new technique is very useful in obtaining a clean regrowth interface even if the regrowth is on AlGaAs. We have demonstrated an optoelectronic AlGaAs/GaAs hetero-transverse-junction semiconductor device fabricated by this regrowth process. The device operates as not only a laser with a threshold current of 19 mA at room temperature but also as a junction field effect transistor with a transconductance of 120 mS/mm (6.0 μm wide active region and 200 μm long cavity).

Current confinement and leakage currents in planar buried-ridge-structure laser diodes on n-substrate

An electrical device model for the planar buried-ridge-structure laser on n-type substrate is discussed. It takes into account the finite p-type contact resistivity, the two-dimensional current spreading, and the electron leakage current by drift and diffusion. Using this model, the influence of the relevant device parameters on the leakage current in InGaAsP/InP devices emitting at 1.3 mu m is investigated. It is shown that leakage currents are negligible at room temperature if the contact stripe width does not exceed the sum of the active region width and the p-type confinement layer thickness, but they increase markedly with broader contact stripes and with contact resistivities above 10/sup -5/ Omega -cm/sup 2/. The most important parameter influencing the leakage currents is the doping level of the P-InP confinement layer. With a p-type doping level of 1*10/sup 18/ cm/sup -3/, a p-type contact resistivity below 10/sup -5/ Omega -cm/sup 2/ and a contact stripe width of 6 mu m, the model calculations predict a maximum operation temperature exceeding 100 degrees C. This agrees fairly well with experimental data proving that the rather simple planar buried-ridge-structure laser performs as well as more sophisticated devices incorporating current-blocking layers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-threshold quantum well lasers grown by metalorganic chemical vapor deposition on nonplanar substrates

Low-threshold quantum-well lasers having as-grown optical and electronic confinement fabricated by a single-step growth on nonplanar substrates are discussed. Several devices using various approaches for delineating narrow active regions by this technique are described. Fully planar index-guided arrays grown over a nonplanar substrate exhibit a threshold current of 8 mA per element. A technology called temperature engineered growth, which permits the formation of submicrometer active-region widths and wide contacting regions in the same growth step, is introduced. Lasers having active regions as narrow as 0.5 mu m grown using this technology display stable single-transverse-mode operation. CW threshold currents as low as 2.5 mA at room temperature with differential quantum efficiencies of 34%/facet were measured for uncoated devices. >

InGaAs-GaAs strained-layer quantum well buried heterostructure lasers (λ&amp;gt;1 μm) by metalorganic chemical vapor deposition

Data are presented on long-wavelength (λ&amp;gt;1 μm) strained-layer InGaAs-GaAs quantum well buried heterostructure lasers grown by a two-step metalorganic chemical vapor deposition (MOCVD) process. Wet chemical etched mesas with an active region width of 3.5 μm are formed in a step-graded InGaAs-GaAs quantum well structure using an oxide mask. Selective MOCVD regrowth is used to form the buried heterostructure. Data are presented for devices having output powers of greater than 130 mW/facet, pulsed threshold currents of less than 7 mA, and internal quantum efficiencies of greater than 60%, for an emission wavelength of 1.074 μm. The near-field patterns indicate stable index-guided fundamental mode operation to greater than 30Ith.

Temperature engineered growth of low-threshold quantum well lasers by metalorganic chemical vapor deposition

A new technique is demonstrated for the formation of narrow active regions in quantum well lasers. In temperature engineered growth (TEG), the substrate temperature is varied during the growth of epitaxial layers by metalorganic chemical vapor deposition (MOCVD) on nonplanar substrates, allowing two-dimensional control of device features. Buried heterostructure designs with submicron active region stripe widths are obtained without the need for fine process control of lateral dimensions. The contact area above the active region is coplanar with the surrounding surface and wide enough to allow easy contacting and heat sinking. Carrier confinement is accomplished by lateral thickness variation of the quantum well active region resulting in a local strip of minimum band gap. Lasers grown in this manner exhibit cw threshold currents as low as 3.8 mA (3.4 mA pulsed), having an as-grown active region width of 0.5 μm. The near-field optical profile indicates stable, single transverse mode operation and minimal current leakage in these devices.

New fabrication method for 1.3-μm GaInAsP/InP buried crescent lasers using a reactive ion beam etching technique

A 1.3-μm GaInAsP/InP buried crescent laser on a p-type InP substrate was demonstrated. An active region width narrower than 1.5 μm was achieved with good controllability and reproducibility using the newly introduced reactive ion beam etching technique for the etching process. Stable fundamental transverse mode operation with low threshold currents of 15–25 mA was obtained. Less than 5% degradation in threshold current at 50 °C was achieved with a constant driving current of 150 mA at 70 °C for 100 h.

Opto-electronic device structures fabricated by impurity induced disordering

Over the past several years, metalorganic chemical vapor deposition (MOCVD) has become established as a viable technique for the fabrication of the thin quantum well layers required for efficient light emitting structures in the AlGaAs system. By combining the MOVCD growth technique with novel device processing via impurity induced disordering (IID), efficient, low threshold buried heterostructure lasers have been produced. IID has been investigated by the diffusion of both zinc and silicon, and it has been found that silicon disordering is more effective in creating the abrupt transitions between ordered and disordered materials required for low threshold laser structures. The optical and electronic confinement achieved by the IID technique have been shown to be sufficiently strong to produce semiconductor lasers with threshold currents approaching 1 mA in a device with a 1–2 μm wide lasing filament. Similar structures with a 7 μm wide active region have produced up to 80mW of continuous power. A conversion efficiency of more than 40% has been achieved with IID in single emitter devices at 25mW and multiple (10) emitter devices at 250 mW. The single emitter versions of these devices operate in a single longitudinal mode, with adjacent modes supressed by more than 22 dB. Preliminary lifetesting data on single emitter devices indicate lifetimes to be in the tens of thousands of hours. Thus it appears certain that the IID technique will become of increasing interest in the fabrication of future optoelectronic devices.