Showing papers by "Stephen J. Pearton published in 1991"

Stability of carbon and beryllium‐doped base GaAs/AlGaAs heterojunction bipolar transistors

Abstract: GaAs/AlGaAs heterojunction bipolar transitors (HBTs) utilizing highly Be‐doped base layers display a rapid degradation of dc current gain and junction ideality factors during bias application at elevated temperature. For example, the gain of a 2×10 μm2 device with a 4×1019 cm−3 Be‐doped base layer operated at 200 °C with a collector current of 2.5×104 A cm−2 falls from 16 to 1.5 within 2 h. Both the base emitter and base collector junction ideality factors also rise rapidly during device operation, and this current‐induced degradation is consistent with recombination‐enhanced diffusion of Be interstitials producing graded junctions. By sharp contrast, devices with highly C‐doped (p=7×1019 cm−3) base layers operated under the same conditions show no measurable degradation over much longer periods (12 h). This high degree of stability is most likely a result of the fact that C occupies the As sublattice, rather than the Ga sublattice as in the case of Be, and also has a higher solubility than Be. The effect of nearby implant isolated regions in promoting Be diffusion is also reported.

Hydrogen diffusion in crystalline semiconductors

Abstract: The diffusion of hydrogen in semiconductors is complicated by the existence of several charge states (notably H+ in p-type material and H- or H0 in n-type material, at least for Si) and also that hydrogen is present in a number of different forms, namely atomic, molecular or bound to a defect or impurity. Since the probability of formation of these different states is dependent on the defect or impurity type and concentration in the material and on the hydrogen concentration itself, then the apparent hydrogen diffusivity is a function of the sample conductivity and type and of the method of hydrogen insertion. Under conditions of low H+ concentration in p-type Si, for example, the diffusivity is of the order of 10-10 cm2 · s-1 at 300 K and is consistent with the value expected from an extrapolation of the Van Wieringen and Warmoltz expression DH = 9.4 × 10-3exp[-0.48 eV/kT] cm2 · s-1. The characteristics of hydrogen diffusion in n- and p-type Si and GaAs are reviewed in this paper, and the retardation of hydrogen permeation by molecular formation and impurity trapping is discussed. The measurement of several key parameters, including the energy levels for the hydrogen donor and acceptor in Si and the diffusivity of the H0 and H- species, would allow a more quantitative treatment of hydrogen diffusion in semiconductors.

Properties of titanium nitride thin films deposited by rapid‐thermal‐low‐pressure‐metalorganic‐chemical‐vapor‐deposition technique using tetrakis (dimethylamido) titanium precursor

Abstract: Titanium nitride (TiNx) thin films were deposited onto InP by means of the rapid‐thermal‐low‐pressure‐chemical‐vapor‐deposition (RT‐LPMOCVD) technique, using the tetrakis (dimethylamido) titanium (Ti(NMe2)4 or DMATi) complex as the precursor. Depositions were successfully carried out at temperatures below 550 °C, pressure range of 5–20 Torr and duration of 50 to 90 s, to give layer thicknesses up to 200 nm and growth rates in the range of 0.8 to 4.5 nm/s. These films had a stoichiometric structure and contained nitrogen and titanium in a ratio close to unity, but also contained a significant amount of carbon and oxygen. The elements were spread uniformly through the films, the nitrogen was Ti bounded, and the carbon was partially titanium bonded and organic bonded as well. The film resistivity was in the range of 400–800 μΩ cm−2; the stress was always compressive, in the range of − 0.5 × 109 to − 2 × 1010 dyne cm−2, and the film had a good morphology. These layers performed as an ohmic contact while deposited onto p‐In0.53Ga0.47As material, (Zn‐doped 1.2 × 1018 cm−3), provided an excellent step coverage for high aspect ratio via holes and were deposited selectively onto the InP and based materials when using SiO2 mask. This represents the first report of TiNx films deposited in a commercial RT‐LPMOCVD reactor using the DMATi precursor.

Thermal stability of dopant‐hydrogen pairs in GaAs

Abstract: The thermal stability of dopant‐hydrogen complexes in hydrogenated n‐ and p‐type GaAs(1–2×1017 cm−3) has been determined by examining their reactivation kinetics in reverse‐biased Schottky diodes. The reactivation process is first‐order for all of the dopants, with thermal dissociation energies (ED) of 1.45±0.10 eV for SiAs acceptors, 1.25±0.05 eV for SiGa donors, 1.20±0.10 eV for SnGa donors, 1.25±0.10 eV for Zn acceptors, 1.35±0.05 eV for CAs acceptors, and 1.15±0.10 eV for Be acceptors. The dissociation frequencies (ν) are thermally activated of the form νD = ν0E−ED/kT, with the ν0 values in the range 1–5×1013 s−1. The results are consistent with much of the H being present as H+ in p‐type material, and H− in n‐type material.

Ion implantation doping and isolation of III–V semiconductors

Abstract: Ion implantation is used for two purposes in III–V materials — to create doped regions that act as active channel layers or contacts or to create high-resistivity regions that provide device isolation. We review the key areas associated with damage removal and dopant activation in binary (GaAs, InP) and ternary (AlGaAs, InGaAs, AlInAs) compounds. In particular recent results on the behavior of implanted carbon in these materials sheds new light on puzzling past data on more conventional light dopants such as Be. The production of high-resistance regions in Ga- and In-based materials resulting from radiation damage that traps free carriers will also be reviewed. In the Ga-based materials the Fermi level becomes pinned at midgap for either n-type or p-type samples, and resistivities ≥ 107 Ω cm can he achieved. By contrast, in InP the Fermi level moved into the upper half of the band gap and initially n-type material shows a limiting resistivity of 103−104 Ω cm. The differences between damage-induced and chemically induced compensation will be detailed.

Selfaligned AlGaAs/GaAs HBT grown by MOMBE

Abstract: The very low parasitic resistance n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBT) grown by metal organic molecular beam epitaxy (MOMBE) using all gaseous source dopants are reported. The carbon and tin dopants were introduced through the uses of trimethygallium (TMGa) and tetraethyltin (TESn). To achieve the low parasitics, the graded InGaAs emitter cap layer was doped with tin to 5*10/sup 19/ cm/sup -3/ and the doping level in the subcollector was 3*10/sup 18/ cm/sup -3/. The emitter and collector sheet resistances were 25 Omega / Square Operator and 10 Omega / Square Operator , respectively. The 800 AA thick base layer was carbon doped to a level of 7*10/sup 19/ cm/sup -3/. The base contact resistance and sheet resistance were 0.1 Omega mm and 180 Omega / Square Operator , respectively. With a thin AlGaAs surface passivation layer for the emitter-base junction, the common emitter DC current gain was maintained up to 25, even for 2*5 mu m/sup 2/ emitter size devices. The unity short circuit current gain cutoff frequency f/sub T/, and maximum oscillation frequency f/sub max/, were 48 and 63 GHz, respectively.

Measurement of electron densities in electron cyclotron resonance plasmas for etching of III‐V semiconductors

Abstract: The average electron densities in CH4/H2/Ar and CCl2F2/O2 electron cyclotron resonance discharges typical of those used for etching InP, GaAs, and related materials have been measured approximately 4 cm downstream from the multipolar microwave source as a function of microwave power (50–300 W), additional radio‐frequency power (10–50 W), pressure (1–20 mTorr), flow rate (30–90 standard cubic centimeters per minute) and gas composition. At 1 mTorr pressure and 10 W rf, the electron densities (and semiconductor etch rates) increase rapidly with microwave power, from 1.3×1011 cm−3 for 5CH4/17H2/8Ar and 6×1010 cm−3 for 28CCl2F2/2O2 discharges at 50‐W microwave power, to 9×1011 cm−3 and 3×1011 cm−3, respectively at 300‐W microwave power. At the highest microwave power levels (≥200 W) the InP and GaAs etched surface morphologies are rough due to preferential removal of one of the lattice constituents from each material. The electron densities in both types of discharge show moderate increases with increasing rf...

Dry-etching techniques and chemistries for III–V semiconductors

Abstract: Dry etching of III–V materials using both chlorine-based (CCl2F2, SiCl4, BCl3 and Cl2) and CH4-H2 discharges is briefly reviewed. The etch rates using chlorine-based mixtures are generally faster than those utilizing CH4-H2, but the latter gives smoother surface morphologies for indium-containing compounds. The use of microwave (2.45 GHz) electron cyclotron resonance (ECR) discharges minimizes the depth of lattice disorder resulting from dry etching, relative to conventional r.f. (13.56 MHz) discharges. Recent results on the systematics of ECR plasma etching of both indium- and gallium-based III–V semiconductors using CCl2F2-O2 and CH4-H2 mixtures will be discussed, including the determination of the maximum self-biases allowable which do not induce near-surface damage in the semiconductor. A further key issue is the prevention of changes in the surface stoichiometry of materials such as InP, where the lattice constituents may have considerably different volatilities in the particular discharge.

High-power 980-nm AlGaAs/InGaAs strained quantum-well laser grown by OMVPE

Abstract: High-power lattice-strained AlGaAs/InGaAs graded index separate-confinement heterostructure (GRINSCH) quantum-well lasers emitting at a 980-nm wavelength have been grown by organometallic vapor phase epitaxy (OMVPE) and fabricated with a self-aligned ridge-waveguide structure. Using a 3- mu m-wide and 750- mu m-long AR-HR coated laser, 30 mV of optical power was coupled into optical fibers with 28.6% efficiency. A dominating single-lobe far-field radiation pattern was obtained from a wedge-shaped ridge-waveguide laser for output power as high as 240 mW with a maximum output power of 310 mW. >

Carbon and tin doped npn and pnp AlGaAs/GaAs HBTs grown by MOMBE

Abstract: High performance, selfaligned processed npn and pnp AlGaAs/GaAs HBTs grown by MOMBE are reported. Tin and carbon were used as n- and p-type dopants, respectively. Cutoff frequency and maximum frequency of oscillation of 53 and 128 GHz, respectively, were obtained for npn transistors (2×5 μm2 emitter) and values of 30 and 12 GHz, respectively, were measured for pnp transistors (2×4 μm2 emitter).

10 Gbit/s AlGaAs/GaAs HBT driver IC for lasers or lightwave modulators

Abstract: A 10 Gbit/s driver IC for lasers or lightwave modulators has been implemented using carbon-doped base AlGaAs/GaAs HBTs. The integrated circuit is intended for applications involving either direct or external modulation of laser sources. The circuit is capable of driving 60 mA into a 50Ω load with rise/fall times of 40 ps and generates a differential output voltage of 6 V peak to peak at 10 Gbit/s. Modifying the design slightly, a 9 V peak to peak differential output was achieved at 5 Gbit/s by switching 90 mA into a 50Ω load.

Improvement of ohmic contacts on GaAs with in situ cleaning

Abstract: An in situ argon ion mill clean step prior to ohmic metal deposition has been demonstrated to improve the uniformity of the contact parameters and reduce the contact resistance. After ion mill cleaning, the native oxide regrowth of molecular beam epitaxy grown GaAs and AlGaAs layers in vacuum chamber was also studied to optimize the processing. These oxide layers were identified as the cause of problems in the formation of good ohmic contacts to the GaAs or AlGaAs.

Method for forming patterned tungsten layers

Abstract: The present applicants have discovered that a layer predominantly comprising tungsten can be formed into precise patterns having substantially vertical walls by using titanium as a mask and plasma etching in a fluorine-containing plasma such as CF4 or SF6. The success of the process is believed attributable to the occurrence of an etch stop reaction on the sidewalls of the tungsten. The products of the reaction inhibit horizontal etching. After the tungsten is etched, the titanium mask can be selectively removed, as by etching in dilute HF. Each step in the process can be effected without subjecting the workpiece to voltage magnitudes in excess of 200 volts or temperatures outside the range between room temperature and 200° C.

AlInAs/InGaAs based heterojunction bipolar transistors fabricated by electron cyclotron resonance etch

Abstract: A dry etch fabrication technology for high‐speed AlInAs/InGaAs heterojunction bipolar transistors (HBTs) utilizing low‐damage electron cyclotron resonance (ECR) CH4/H2/Ar plasma etching is detailed. Small‐area (2×4 to 3×9 μm2 ) devices demonstrated current gains up to 160, unity gain cutoff frequency ( fT) of 57 GHz and a maximum oscillation frequency ( fmax) of 35 GHz. The dry etch process uses triple self‐alignment of the emitter and base metals and the base mesa, minimizing the base‐collector capacitance (CBC). These results represent the first report of a truly scalable process for In‐based HBTs and demonstrate the ability of ECR plasma etching to provide smooth, degradation‐free etching of III–V semiconductors.

Sidewall roughness during dry etching of InP

Abstract: A common feature of mesa structures formed by dry etching of III-V materials is the presence of corrugations or ribbing on the mesa sidewalls. The authors show that this sidewall roughness results from a replication of the roughness present at the edges of the masking material on the semiconductor. Using a photoresist mask free of sidewall roughness they demonstrate that it is possible to achieve a completely smooth mesa in InP with CH4/H2/Ar plasma etching. This is particularly important in minimizing light scattering in certain types of long wavelength lasers. It is also shown that the mask sidewall roughness does not worsen during the plasma exposure, even for long (2 h) etching runs.

Self‐aligned technology for tungsten‐contacted InP‐based etched mesa laser devices

Abstract: The characteristics of W metallization for use as self‐aligned ohmic contacts and selective area etching and regrowth masks on InP‐based laser structures are reported. rf‐sputtered W films under either compressive or tensile stress were examined. Mesas for epitaxial regrowth were obtained by CF4/O2 dry etching of the previously deposited W film, followed either by HBr/H2O2/H2O wet chemical etching or CH4/H2/Ar electron cyclotron resonance plasma etching of ∼4 μm of InP. The W film preserved its inert metallurgical nature while heated under PH3/H2 ambient at 700 °C for 20 min, simulating the standard regrowth conditions. The W contacts on n‐InP (n=5×1018 cm−3) substrates yielded stable, low contact resistivity (0.2 Ω cm) after rapid thermal processing at 600–700 °C.

Use of ultraviolet/ozone cleaning to remove C and O from GaAs prior to metalorganic molecular beam epitaxy and metalorganic chemical vapor deposition

Abstract: Ultraviolet/ozone cleaning of GaAs substrates prior to metalorganic molecular beam epitaxy at 500 °C is shown to reduce the interfacial C and O concentrations by more than two orders of magnitude Metal‐semiconductor field‐effect transistors (MESFETs) utilizing this cleaning prior to growth of the component epitaxial layers display superior current voltage (I‐V) saturation characteristics compared to identical devices grown without the cleaning step By contrast, provided the GaAs surface is not contaminated with silicates, the atomic hydrogen generated at the growth surface during growth by metalorganic chemical vapor deposition (MOCVD) leads to lower O and C interfacial concentrations, thereby circumventing the need for ozone cleaning MESFETs grown by MOCVD with or without this cleaning have excellent I‐V characteristics

Dissociation of P‐H, As‐H, and Sb‐H complexes in n‐type Si

Abstract: Reverse‐bias annealing of P‐H, As‐H, and Sb‐H pairs in hydrogenated Schottky diodes was used to establish the dissociation energies of these complexes. The annealing kinetics are found to be first order, with the dissociation frequencies thermally activated of the form ν=ν0e−ED/kT. The dissociation energies ED are found to be 1.20±0.05 eV for P‐H, 1.12±0.05 eV for As‐H, and 1.13±0.05 eV for Sb‐H. The relative insensitivity of these values to the actual donor species is consistent with the currently accepted model in which the hydrogen passivates the electrical activity of the donor by attaching to one of the donors Si nearest neighbors at an antibonding interstitial site.

Improved breakdown of AlInAs/InGaAs heterojunction bipolar transistors

Abstract: AlInAs/InGaAs heterojunction bipolar transistors exhibiting DC breakdown voltages, Vceo, in excess of 7 V are reported. The layer structure uses a two-stage collector to achieve the high breakdown voltages. The devices are fabricated with a triply selfaligned dry etch process with high yield. Respective fτ and fmax values of 80 and 60 GHz are obtained for emitter dimensions of 2×4 μm2. The combination of layer structure design and processing yields AlInAs/InGaAs with both DC and RF characteristics suitable for large-scale, high-speed digital circuit applications.

Growth and dry etch processing of MOMBE GaAs p-n junctions

Abstract: p-n GaAs junctions grown by metal-organic molecular beam epitaxy (MOMBE) utilizing carbon and tin derived from gaseous sources are demonstrated. The dopants exhibit sharp profiles with no cross-contamination into adjacent layers. Ideality factors of 1.55 were obtained for both n-on-p and p-on-n diodes, with an absence of low-bias recombination current. Simultaneous exposure of both the n- and p-type layers to O2 or H2 discharges produces increases in the respective sheet resistances which are functions of the DC bias on the sample during the plasma exposure and of the exposure time. Significant changes in the ideality factor of an n-on-p junction are only observed for O+ or H+ ion energies above -200 V. Hydrogen passivation effects can be removed by annealing at 400 degrees C, but high energy (>or=300 eV) O+ ion bombardment causes irreversible damage to the diode.

Electron cyclotron resonance plasma‐induced damage in AlGaAs/GaAs/AlGaAs single quantum wells

Abstract: Changes in cathodoluminescence (CL) intensity from a buried single AlGaAs/GaAs/AlGaAs quantum well (QW) as a result of exposure to electron cyclotron resonance (ECR) hydrogen or argon discharges are reported. For additional dc biases of 150 V on the sample during either H2 or Ar plasma exposure, we observe substantial decreases in CL intensity from the well. Ar+ ion bombardment creates damage more resistant to annealing than does H+ ion bombardment at the same energy. The ECR discharges alone with zero additional dc bias cause degradation in the well luminescence due possibly to defects created by energetic electron bombardment or ultraviolet illumination. At intermediate bias voltages (50 V) strong hydrogen passivation of nonradiative centers is observed, leading to 500% increases in CL intensity from the well. The initial characteristics of the QW under these conditions are restored by annealing at 400 °C.

GaAs/AlGaAs quantum well and modulation‐doped heterostructures grown by organometallic vapor phase epitaxy using trimethylamine alane

Abstract: High‐quality GaAs/AlGaAs quantum well and modulation‐doped heterostructures have been grown by low‐pressure organometallic vapor phase epitaxy (OMVPE) using trimethylamine alane (TMAA) as a new aluminum source. TMAA is an alternative to the conventional organometallic precursors and offers the advantage of substantially reduced oxygen and carbon incorporation in AlGaAs. Intense photoluminescence (PL) with narrow linewidths at 2 K was observed from multiple quantum well samples with well widths of 1.5–10 nm. Transmission electron microscopy of a fifty period superlattice (4 nm GaAs/44 nm Al0.18Ga0.82As) revealed abrupt interfaces and excellent well‐to‐well thickness uniformity. Selectively doped heterostructure transistors (SDHTs) fabricated on the modulation‐doped structures exhibited a maximum extrinsic transconductance of 339 mS/mm for a 1‐μm‐gate length at 300‐K, the highest reported for OMVPE grown devices. A unity current gain cutoff frequency, ft, of 16 GHz and a maximum frequency of oscillation, fm...

Degradation-free electron cyclotron resonance plasma etching of InP

Abstract: The authors report the first demonstration of featureless surface morphology on InP plasma etched in CH4/H2/Ar electron cyclotron resonance (ECR) discharges. At a plasma composition of 5 CH4/17 H2/8 Ar it is necessary to limit the microwave input power to or=3 compared with CH4/H2 alone, indicating that some additional degree of ion bombardment is necessary with this gas chemistry even under ECR conditions. Degradation of the InP photoluminescence as a result of plasma etching at bias voltages less than 150 V can be completely quenched by the addition of PCl3 to the discharge. This provides a phosphorus partial pressure during the etch, maintaining the stoichiometry of the InP surface.

Characteristics of Be+ and O+ or H+ co‐implantation in GaAs/AlGaAs heterojunction bipolar transistor structures

Abstract: The simultaneous formation of buried external collector and extrinsic base regions in GaAs/AlGaAs heterojunction bipolar transistor (HBT) structures by co‐implantation of Be+ together with O+ or H+ ions is described. Oxygen implants at doses of ≥ 1012 cm−2, or proton implants at doses ≥ 1014 cm−2, followed by annealing at 500–550 °C, create fully depleted collector regions, while similar anneals lead to significant Be activation and lowered base resistance. Higher annealing temperatures improve this Be activation but restore the initial doping level in the implanted collector region. For Be+ ion doses ≤ 5≤5× 1014 cm−2 there are no defects visible by transmission electron microscopy in the HBT structure for annealing temperatures below 800 °C.

10 Gbit/s high sensitivity low error rate decision circuit implemented with C-doped AlGaAs/GaAs HBTs

Abstract: A 10 Gbit/s decision circuit has been implemented using AlGaAs/GaAs HBTs with a carbon doped base region. The circuit has an ambiguity level of 27 mV peak to peak with a 240° phase margin at 10 Gbit/s. The error ratio was less than 10−14 for 100 mV peak to peak input data using a 223−1 PRBS.