GaAs Diodes Research Articles

Efficient III–V tunneling diodes with ErAs recombination centers

We report on recombination diodes containing monolayer depositions of ErAs between highly doped n- and p-layers in the (Al)GaAs and In(Al)GaAs material system. The ErAs material provides metallic states across the band gap of the host semiconductor that act as efficient recombination centers. Both electrons and holes can tunnel into the ErAs, resulting in extremely high tunneling current densities in the tens of kA cm−2 range. A device resistance area product of 1–2 × 10−5 Ω cm2 at low bias (±0.2 V) has been measured. Measurements on In(Al)GaAs and (Al)GaAs diodes will be compared to a simple theoretical model. Low band gap and high (p-) doping levels are identified as key parameters for achieving highest recombination currents. Compared to ErAs-free diodes, ErAs-enhanced recombination diodes provide orders of magnitude higher current densities at both moderate and low forward and reverse bias. This is attributed to the smaller and narrower tunnel barriers from the n- and p-layers into the ErAs compared to tunneling from the n- to the p-side through the whole depletion region.

A Deep Level Transient Spectroscopy Study of Electron and Proton Irradiated ${\hbox {p}} ^{+} {\hbox {n}}$ GaAs Diodes

Defects produced by 0.6 MeV, 1 MeV, and 5 MeV electrons are compared with those produced by 2 MeV proton irradiations in p+n GaAs diodes using Deep Level Transient Spectroscopy (DLTS). The introduction rates are determined as a function of electron energy and compared with the nonionizing energy loss (NIEL). It has been determined that a majority of the electron-induced defects (E-traps) are similar to those observed following proton irradiation (PR-traps). However, a new defect emerges in the 5 MeV electron DLTS spectrum with a peak maximum occurring at ∼ 163 K which is not observed at the other electron energies. It has been determined that this new electron-induced defect which has previously not been detected is the proton-induced PR4'' defect. This defect emerges as the incident electron energy is increased suggesting it is formed by higher energy recoils and may be a complex defect. The recoil spectra are analyzed.

MONTE CARLO SIMULATION OF STEADY-STATE TRANSPORT IN SUBMICROMETER InP AND GaAsn+–i(n)–n+ DIODE

Monte Carlo simulation of electron transport in an InP diode of n+–i(n)–n+ structure is compared with GaAs diode. The anode voltage ranges from 0.5 to 1.5 V. The distributions of electron energies and electron velocities and the profiles of the electron density, electric field and potential and average electron velocity are computed. Based on these data, the near ballistic nature of the electron transport in the 0.2 μm-long diode and the importance of the back-scattering of electrons from the anode n+-layer are discussed. In addition, the effects of the lattice temperature and doping on the length of the active layer are discussed. Electronic states within the conduction band valleys at the Γ, L, and X are represented by non-parabolic ellipsoidal valleys centered on important symmetry points of the Brillouin zone. Our simulation results have also shown that the electron velocity characteristics in InP diode are more sensitive to temperature than in other III–V semiconductors such as GaAs .

The Use of Surgical Diode Laser in Oral Hemangioma: A Case Report

To review the literature regarding the use of surgical lasers in hemangioma treatment and to report a clinical case involving diode laser. Hemangiomas are benign vascular proliferations consisting of numerous capillary structures and are especially common on the tongue, lips, jugal mucous membrane, and gums. A number of treatment modalities have been proposed for hemangioma treatment. The patient was referred for evaluation complaining of chewing difficulty because of swelling in the right area of the upper lip, with no previous trauma. The lesion was located in the internal right jugal mucous membrane, measured 4 x 4 cm(2), presented a bluish coloration, and was diagnosed as a hemangioma. The treatment selected was surgical removal using gallium arsenide (GaAs) diode laser at 980 nm wavelength, with 4.0 W of power. During surgery, complications including hemorrhage were not observed, and no scarring developed after surgery. The use of GaAs high-potency diode laser in the treatment of hemangioma reduced bleeding during surgery, with a consequent reduction in operating time, and promoted rapid postoperative hemostasis. It is safe for use on large lesions and easy to manage, and postoperative problems, including potential scarring, and discomfort are minimal.

Lasers in Periodontics: An Overview

ABSTRACT Among commonly used lasers in dentistry viz CO2, Nd:YAG, Ho:YAG, Er: YAG, Er, Cr:YSGG, Nd:YAP, GaAs (diode) and argon, Er:YAG laser, at appropriate settings, possesses the best property for selective subgingival calculus removal without a thermal change of the root surface, soft tissue surgical procedures, root surface alterations, degranulation and implant surface decontamination alongwith proposed application in osseous surgery. Epithelial exclusion using CO2 laser has been suggested to retard its downward growth. Waterlase® and PeriowaveTM systems are recent devices that have further revolutionised the laser techonology for its favourable clinical applications; however, the procedural cost with the laser device still constitutes an obstacle for its routine application.

LPE technology for power GaAs diode structures

A liquid phase epitaxy technology for deposition of GaAs epilayers on the monocristallic GaAs substrates for high voltage ultra fast power p + -p-i-n-n + GaAs structures has been developed. Proposed technological and hardware solutions of the LPE allow high efficiency of the growing process of diode structures with prescribed ratings and high structural quality of epitaxial layers. A method and technology for the fabrication of GaAs dies for the nanosecond range with reverse voltage up to 1200 V and current up to 100 A in diode chips is introduced. Reverse recovery times down to 20 ns were achieved and could be preserved up to + 260 ° .

Development of a cryogenic duplexer for solid-state nuclear magnetic resonance

To fully appreciate sensitivity enhancement achievable by reducing thermal noise at the detection coil for nuclear magnetic resonance (NMR), a duplexer operational at low temperature is required. In this work, we developed a cryogenic duplexer that can work below 50 K using GaAs diodes and rf-microelectrical mechanical systems switches. As the observed leakage of a rf pulse (100 W and 50 micros) through the duplexer is below 1 mW, it can be used not only for NMR in liquids but also for NMR in solids. We reported recently the cryocoil magic-angle spinning (MAS) probe [T. Mizuno et al., Rev. Sci. Instrum. 79, 044706 (2008)] into which was incorporated with this duplexer and a commercial rf preamplifier, we show that signal-to-noise ratio gain of 4.0 times can be achieved for (1)H MAS-NMR by lowering the detection-coil temperature to 12 K and the temperatures for the rf preamplifier and the duplexer to 43 K.

Characterization of GaAs grown on SiGe/Si graded substrates using p-n junction diodes

The effect of GaAs buffer thickness on the electrical characteristics of a p+-n− junction diode is presented. The GaAs diodes are grown on a Ge/graded SixGe1−x/Si virtual substrate. Electrical characterization and visual observation provided vital insights into the origin of improvement in the electrical characteristics of the diode as the GaAs buffer thickness is increased. A high breakdown voltage of −9.2 V was achieved as the buffer thickness was increased from 50 to 600 nm, as the ideality factor reduces from 2.2 to 1.7, indicating reduction in the recombination current in the depletion region. This improvement is found to be related to the suppression mechanism of the wedge-shaped dislocation formation in the growth direction. This evidence provides important insights for the integration of III-V semiconductor devices, such as heterojunction bipolar transistor, with Si-based substrates.

Ballistic electron mean free path of titanylphthalocyanine films grown on GaAs

AbstractIn this article, Au/titanylphthalocyanine/n‐GaAs diodes incorporating ultrathin films of the archetypal organic semiconductor titanylphthalocyanine were investigated by ballistic electron emission microscopy/spectroscopy (BEEM/S). BEEM/S measurements were used to determine the transmission of ballistic electrons through titanylphthalocyanine as a function of energy and temperature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influência de diferentes comprimentos de onda da laserterapia de baixa intensidade na regeneração tendínea do rato após tenotomia

Influence of different low-intensity laser therapy wavelengths for rat tendon regeneration following tenotomy Objective: The aim of this study was to compare the effect of the low level laser therapy in the organization of the collagen fibers with 3 J/cm² of dose in two wavelengths (670nm and 904nm) and in the combination of both on the tissue repair of the calcaneus tendon. Methods: We used 37 female Wistar rats divided in 5 groups which had been submitted to the total tenotomy. Group GA (n= 8) was submitted to the laser irradiation in λ= 904nm, GaAS diode, pulsated emission, peak power 15W and dose of 3J/cm², group GB (n= 8) was submitted to laser irradiation λ= 670nm AlGaInP diode, continuous emission, power 30 mW and dose 3J/cm², group GAB (n= 8) was submitted to association of both of lasers and group GCL (n= 7) which the calcaneum tendon was submitted to placebo treatment. The group GP (n= 6) was a standard group without lesion and treatment. The animals received 12 sessions of lasertherapy and submitted to euthanasia on 14 th day after surgery. The tendons were submitted to histological procedure and were analyzed to evaluate the optic retardation (in nm) for the birefringence measurement. Results: The statistic analysis showed that the irradiated groups have higher values of optic retardation statistically significant than placebo group (p= 0,00001). It indicates that all the treated groups show better organization of collagen fibers in the longitudinal axis of the tendon, evidencing better quality in the tissue repair. The group GAB was that shown best results (p= 0,00001) when compared to another groups.

Ballistic electron and photocurrent transport in Au-molecular layer-GaAs diodes

We present a study on hot electron transport through Au∕molecule∕n-GaAs(001) diodes via ballistic electron emission microcopy (BEEM). The molecules in the structure form a monolayer of either octanedithiol [HS–(CH2)8–SH] or hexadecanethiol [HS–(CH2)15–CH3]. For the dithiol case, the presence of the molecular interlayer leads to undetectable BEEM transmission. Whereas a small photoinduced collector current is detected at random locations at a forward (reverse) scanning tunneling microscopy (STM) tip voltage of −1.43±0.01V (+1.50±0.02V). In comparison, with monothiol diodes, or diodes where the molecules are sandwiched between two Au films (Au∕molecule∕Au∕GaAs), the BEEM transmission remains a significant fraction of the reference diode signal (30%–80%) with a slight increase in the ballistic transport threshold voltage (−1.0to−1.1V) from that of the reference Au∕GaAs diodes (−0.89V). Auger depth profiling and cross-sectional transmission electron microscopy show that Au-molecule intermixing occurs in Au/hexadecanethiol/GaAs but not in Au/octanedithiol/GaAs diodes. The suppression of BEEM signal and the detection of STM-induced photocurrent in the Au/octanedithiol/GaAs case are consistent with an insulating monolayer containing pinholes or recombination centers with densities of 1 every 25×25nm2 or ∼2000μm−2.

Low-Level Laser Therapy Applied Transcranially to Mice following Traumatic Brain Injury Significantly Reduces Long-term Neurological Deficits

Low-level laser therapy (LLLT) has been evaluated in this study as a potential therapy for traumatic brain injury (TBI). LLLT has been found to modulate various biological processes. Following TBI in mice, we assessed the hypothesis that LLLT might have a beneficial effect on their neurobehavioral and histological outcome. TBI was induced by a weight-drop device, and motor function was assessed 1 h post-trauma using a neurological severity score (NSS). Mice were then divided into three groups of eight mice each: one control group that received a sham LLLT procedure and was not irradiated; and two groups that received LLLT at two different doses (10 and 20 mW/cm(2) ) transcranially. An 808-nm Ga-As diode laser was employed transcranially 4 h post-trauma to illuminate the entire cortex of the brain. Motor function was assessed up to 4 weeks, and lesion volume was measured. There were no significant changes in NSS at 24 and 48 h between the laser-treated and non-treated mice. Yet, from 5 days and up to 28 days, the NSS of the laser-treated mice were significantly lower (p < 0.05) than the traumatized control mice that were not treated with the laser. The lesion volume of the laser treated mice was significantly lower (1.4%) than the non-treated group (12.1%). Our data suggest that a non-invasive transcranial application of LLLT given 4 h following TBI provides a significant long-term functional neurological benefit. Further confirmatory trials are warranted.

Ballistic electron transport through titanylphthalocyanine films

In this letter, Au/tanylphthalocyanine/GaAs diodes incorporating ultrathin films of the archetypal organic semiconductor titanylphthalocyanine were investigated by ballistic electron emission microscopy (BEEM)/spectroscopy. The presence of the organic semiconductor increases the BEEM threshold voltage compared to reference Au∕GaAs diodes. The Schottky barrier heights were measured for various temperatures and show an approximately linear increase from 1.2eV at room temperature to 1.5eV at T=10K.

Electrical transport in Mn-doped GaAs pn-diodes

We have studied the effect of magnetic ordering on the electrical transport in magnetic GaAs diodes. The fabricated pn-junctions consist of Mn-doped ferromagnetic layers on top of non-magnetic semiconductor substrates. First the electrical and magnetic properties of the magnetic layers are investigated, which shows that the exchange interaction between the charge carriers and the localized magnetic moments of the Mn-atoms dominates the charge transport at temperatures close to the Curie temperature. In the GaxMn1–xAs/GaAs-p++n++-junctions having heavily doped p- and n-regions, the inter-band tunnelling current shows large dependence on the magnetic ordering. The spin-dependent tunnelling can be explained by a model, where the density of valence band states decreases due to the band splitting caused by the exchange interaction. From the measured decrease of the tunnelling current we estimated the value for the exchange parameter = 2.9 eV. Various explanations for the absence of magnetoresistance in the magnetic diodes with lightly doped non-magnetic regions are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Modeling of Charge Transport in a Hybrid Metal / Organic / Inorganic Device

AbstractA Metal / Organic / Inorganic semiconductor heterostructure was built and characterized in situ under ultra-high vacuum conditions (UHV). The aim was to investigate the influence of a perylene-derivative organic thin film on the transport electronic properties of Schottky Ag / GaAs diodes. The device was studied using a combination of photoemission spectroscopy (PES) and electrical measurements. The obtained results were discussed using the analytical expressions of a trapped charge limited current (TCLC) model.

Controlling Au/n‐GaAs junctions by partial molecular monolayers

AbstractA dipole‐layer approach is adapted to describe the electrostatic potential and electronic transport through metal/semiconductor junctions with a discontinuous monolayer of polar molecules at the metal/semiconductor interface. The effective barrier height of those junctions, which have small pinholes, embedded in a molecular layer, which introduces a negative {positive} dipole (i.e., a dipole whose negative {positive} pole is the one that is closest to the semiconductor surface) on an n‐type {p‐type} semiconductor, is often “tunable” by the magnitude and density of the dipoles. If the lateral dimensions of a molecule‐free pinhole at the interface exceed the semiconductor depletion width, carrier transport is not influenced by the molecular layer and the “effective” barrier height is the nominal metal/semiconductor barrier height. If the molecular layer introduces a positive {negative} dipole on an n‐type {p‐type} semiconductor, enhanced field emission at edges of small pinholes might lead to a leakage‐ and/or an edge‐current component resulting in an effective barrier height lower than the nominal one. We support these conclusions by direct measurements of the nm‐scale electronic behaviour of a Au/n‐GaAs diode with a discontinuous monolayer of dicarboxylic acids at the interface, using Ballistic Electron Emission Microscopy (BEEM). (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Low-Level Laser Therapy Applied Transcranially to Rats After Induction of Stroke Significantly Reduces Long-Term Neurological Deficits

Low-level laser therapy (LLLT) modulates various biological processes. In the present study, we assessed the hypothesis that LLLT after induction of stroke may have a beneficial effect on ischemic brain tissue. Two sets of experiments were performed. Stroke was induced in rats by (1) permanent occlusion of the middle cerebral artery through a craniotomy or (2) insertion of a filament. After induction of stroke, a battery of neurological and functional tests (neurological score, adhesive removal) was performed. Four and 24 hours poststroke, a Ga-As diode laser was used transcranially to illuminate the hemisphere contralateral to the stroke at a power density of 7.5 mW/cm2. In both models of stroke, LLLT significantly reduced neurological deficits when applied 24 hours poststroke. Application of the laser at 4 hours poststroke did not affect the neurological outcome of the stroke-induced rats as compared with controls. There was no statistically significant difference in the stroke lesion area between control and laser-irradiated rats. The number of newly formed neuronal cells, assessed by double immunoreactivity to bromodeoxyuridine and tubulin isotype III as well as migrating cells (doublecortin immunoactivity), was significantly elevated in the subventricular zone of the hemisphere ipsilateral to the induction of stroke when treated by LLLT. Our data suggest that a noninvasive intervention of LLLT issued 24 hours after acute stroke may provide a significant functional benefit with an underlying mechanism possibly being induction of neurogenesis.

Epitaxial Bi∕GaAs diodes via electrodeposition

Epitaxial Bi∕GaAs diodes have been formed by electrodeposition from bismuth nitrate and ammonium sulfate ((NH4)2SO4) aqueous solutions. Bi grows (0001) oriented on both GaAs (111)B and (001) substrates while it tilts 16° to a (011̱8) surface orientation for (011) GaAs. The metal orients in all cases with its {112̱0} planes parallel the GaAs {110} planes. Diodes prepared on (001), (111)B, and (011) wafers have current-voltage barrier heights ΦBIV that vary from 0.74, to 0.76, to 0.83eV (n=1.01–1.11), respectively. These barrier heights straggle values from earlier reports for polycrystalline Bi deposited by ultrahigh vacuum techniques or electrodeposition. Barrier heights measured from high frequency, capacitance-voltage characteristics are higher than the ΦBIV results, 0.06–1.5eV, as a function of the GaAs orientation, increasing in value in order of (011), (001), to (111)B. This is explained by a combination of image force lowering and field emission corrections, and interface state/dipoles that are likely dependent on the GaAs orientation and on the degree of (0001) Bi alignment. These results are supported by cross-sectional transmission electron microscopy investigations indicating abrupt Bi∕GaAs interfaces without evidence of a significant interfacial oxide or reacted layer.

Acoustic wave corrected current-voltage characteristics of GaAs-based structures with Schottky contacts

The effect of ultrasonic treatment (UST) on the current-voltage (I-U) characteristics of Au-TiBx-n-n +-GaAs diode structures has been studied. Upon acoustic loading with an intensity below 2 W/cm2, the character of the UST-induced changes in the reverse branches of I-U curves depends on the predominating mechanism of current transfer. UST at a power density above 2.5 W/cm2 increases the reverse current by one or two orders of magnitude. It is shown that UST favors a significant increase in the homogeneity of the characteristics of devices manufactured using integral heat sink technology.

Gallium-arsenide deep-level materials for THz and [formula omitted] fiber-optic applications

We demonstrate novel materials utilizing semiconductor deep centers for THz applications and 1.5 μ m fiber-optic emitters on GaAs. We achieve the first [J.L. Pan, J.E. McManis, T. Osadchy, L. Grober, J.M. Woodall, P.J. Kindlmann, Nat. Mater. 2 (2003) 375] light-emitting diode (LED) in the material GaAs emitting at 1.5 μ m fiber-optic wavelengths from arsenic-antisite deep levels. This technology enables 1.5 μ m fiber-optic components lattice matched to GaAs ICs. We experimentally demonstrate significant internal optical power (24 mW), efficiency (almost 1%), and available speed (THz) from GaAs deep-level optical emitters. We also achieve the first tunnel diodes explicitly making use of deep-levels in low-temperature-grown (LTG) GaAs. At room temperature, we demonstrate the largest peak current density ( 16 kA / cm 2 ) ever in a GaAs tunnel diode. Our devices also show room-temperature peak-to-valley current ratios greater than 20. We determine the transport mechanisms which limit the peak and valley currents. Finally, we present the first fully analytical eight-band model [J.L. Pan, Opt. Exp. 9 (2001) 796; J.L. Pan, J. Appl. Phys. 92 (2002) 5991] of the deep-center wave function (e.g., symmetry and admixture of atomic orbitals). Our model determines the general optical properties of deep-centers (optical selection-rules and transition strengths) in terms of simple materials properties (band gap energy, Kane dipole, deep-level position) and angular momenta quantum numbers. Thus, our model is applicable in a wide variety of materials, and is in agreement with experiment.