Showing papers by "Stephen J. Pearton published in 1986"

Optically detected carrier confinement to one and zero dimension in GaAs quantum well wires and boxes

Abstract: Carrier confinement to one and zero degrees of freedom has been achieved in artificial quantum well wires and boxes fabricated in the GaAs‐GaAlAs system. Low‐temperature cathodoluminescence measurements show new luminescence lines attributed to transitions arising from ground and excited levels of electrons within these low dimensional structures.

Kinetics of implantation enhanced interdiffusion of Ga and Al at GaAs‐GaxAl1−xAs interfaces

Abstract: The kinetics of implantation enhanced interdiffusion at GaAs‐GaxAl1−xAs interfaces is investigated by cathodoluminescence and transmission electron microscopy. Localized Ga+ implantation leads to enhancement of the interdiffusion by about two orders of magnitude at 950 °C. A complete recovery of the optical quality of the material and local alteration of the band gap is observed after rapid thermal annealing. The role of intrinsic interdiffusion is identified. Control of the interdiffusion kinetics has allowed the fabrication of ultrasmall structures with good optical properties.

Hydrogenation of shallow‐donor levels in GaAs

Abstract: Shallow‐donor levels due to Si, Ge, Sn, S, Se, and Te in GaAs are neutralized by association with atomic hydrogen; Si and Te donors in AlGaAs have also been shown to be neutralized. In contrast, the shallow acceptors Be, Mg, Zn, and Cd in GaAs are relatively unaffected by hydrogenation. The activation energy for recovery of the donor electrical activity is around 2.1 eV for each of the species, but varies as the strength of an isolated hydrogen‐donor species bond. The neutralization depth of the donors is proportional to the inverse square root of donor concentration, and this depth is given as a function of plasma exposure temperature (100–350 °C) and bonding site density (8×1013–1.5×1018 cm−3).

Passivation of deep level defects in molecular beam epitaxial GaAs by hydrogen plasma exposure

Abstract: The effect of hydrogen plasma exposure on the deep level defects present in GaAs grown by molecular beam epitaxy (MBE) has been investigated by deep level transient spectroscopy and by photoluminescence. The three commonly observed defects in MBE grown layers, the M1, M2, and M4 levels, found to be present at a total concentration of 5×1013 cm−3, are completely passivated by exposure to the hydrogen plasma. At low carrier concentration, in samples where surface recombination is suppressed by a thin GaxAl1−xAs cap, passivation of these defects increases photoluminescence efficiency by factors of 30 and 100 at 298 and 77 K, respectively. Defect passivation occurs in addition to the previously reported donor neutralization, but, whereas the latter is removed by a 400 °C, 5 min anneal, the former remains fully effective. Only upon 600 °C, 5 min annealing does the defect level passivation begin to be lost. Thus there is a wide temperature window within which it is possible to regain the carrier concentration without loss of passivation of the deep level defects.

Hydrogen injection and neutralization of boron acceptors in silicon boiled in water

Abstract: Hydrogen injection and neutralization of boron acceptors are observed in p‐type crystalline Si boiled in water. Electrical neutralization of acceptors by hydrogen was measured by capacitance‐voltage profiling of Al‐contact Schottky diodes from material boiled in light or heavy water, and confirmed by secondary ion mass spectrometry depth profiling of deuterium. Boiling 1 Ω cm p‐Si in water for 6 h (dark conditions) shows significant neutralization to ∼1 μm depth; a drastic reduction in neutralization occurs under strong white light illumination. Hydrogen injection efficiency reduces with increasing resistivity and boiling time, the latter effect suggesting that a surface limiting reaction (for example oxidation) may be involved in the generation of injection sites. Field drift of the donorlike, hydrogen‐related neutralizing defect was detected in reverse‐biased diodes.

Photoluminescence study of the shallow donor neutralization in GaAs(Si) by atomic hydrogen

Abstract: Atomic hydrogen in silicon‐implanted GaAs samples is studied by photoluminescence. The near‐band‐gap luminescence of GaAs samples subjected to a hydrogen plasma reveals the neutralization effect of the shallow donors. The photoluminescence intensity increases after hydrogen plasma treatment. However, the donor‐related luminescence is drastically reduced, indicating a smaller shallow donor concentration. After a thermal anneal (400 °C, 15 min), the original intensities of donor‐related lines are restored. We confirm the model of an electrically inactive hydrogen‐donor complex and rule out compensating defects created by the plasma treatment.

Relationship between secondary defects and electrical activation in ion‐implanted, rapidly annealed GaAs

Abstract: The removal of lattice damage and consequent activation by rapid thermal annealing of implanted Si, Se, Zn, and Be in GaAs was investigated by capacitance‐voltage profiling, Hall measurements, transmission electron microscopy (TEM), secondary ion mass spectrometry, and Rutherford backscattering. The lighter species show optimum electrical characteristics at lower annealing temperatures (∼850 °C for Be, ∼950 °C for Si) than the heavier species (∼900 °C for Zn, ∼1000 °C for Se), consistent with the amount of lattice damage remaining after annealing. TEM reveals the formation of high densities (107 cm−2) of dislocation loops after 800 °C, 3 s anneals of high dose (1×1015 cm−2) implanted GaAs, which are gradually reduced in density after higher temperature anneals (∼1000 °C). The remaining loops do not appear to affect the electrical activation or carrier mobility in the implanted layer, the latter being comparable to bulk values.

Local structure of S impurities in GaAs.

Abstract: The local structure of $\mathrm{S}$ implanted in GaAs has been determined by extended x-ray-absorption fine structure by monitoring of the $\mathrm{S}$ $K\ensuremath{\alpha}$ fluorescence yield. The $\mathrm{S}$ first-neighbor shell shows a significant static broadening compared to the $\mathrm{S}$ second- and third-neighbor shells. This indicates two S configurations of approximately equal population: (1) substitutional $\mathrm{S}$ on an As site and (2) a complex formed by $\mathrm{S}$ on an As site and an As vacancy on the second-neighbor shell with a $\mathrm{S}$-first-neighbor distance relaxation of 0.14 \ifmmode\pm\else\textpm\fi{} 0.04 \AA{}. The two-site configuration explains the disparity between implanted $\mathrm{S}$ concentration and net electrical activity.

Effect of crystal stoichiometry on activation efficiency in Si implanted, rapid thermal annealed GaAs

Abstract: A dramatic dependence on crystal stoichiometry has been observed for the donor activation efficiency of low doses of Si ions implanted into undoped semi‐insulating GaAs. Samples from liquid encapsulated Czochralski crystals grown from melts containing As concentrations varying from 47 1/2 to 65 at. % were implanted with 100 keV 29Si ions at a dose of 5×1012 cm−2. Following a rapid, capless annealing cycle (950 °C, 5 s), the surface‐depletion corrected activation efficiency ranged from 26 to 91%, with the higher efficiencies for higher As concentrations. In contrast, co‐implantation of As and Si into standard (50 at. % As) GaAs resulted in an increase in activation efficiency from 59 to 68% for optimum As doses.

Rapid annealing of GaAs: Uniformity and temperature dependence of activation

Abstract: Scanning microwave photoconductance, capacitance‐voltage profiling, and Hall effect measurements were used to investigate the uniformity of activation of Si‐, Be‐, and Mg‐implanted 2‐ and 3‐in.‐diam, semi‐insulating GaAs substrates after rapid thermal annealing in a commerical furnace. The results indicate that carrier lifetimes and mobilities for low‐dose (3–4×1012 cm−2) implants and carrier densities for high‐dose (1×1015 cm−2) implants are comparable or superior in rapidly annealed substrates to those obtained in thermally annealed implanted layers. The uniformity of these parameters is not significantly different for wafers annealed by either method. The temperature dependence of damage removal and carrier activation in the implanted regions during both furnace and transient annealing was also investigated, and demonstrates that the microwave photoconductance technique gives results for donor implantation correlating well with conventional backscattering and electrical measurements, respectively.

Structures including quantum well wires and boxes

Abstract: A method of fabricating quantum well wires and boxes is described in which interdiffusion in a semiconductor having a compositional profile is enhanced by the presence of defects created by ion implantation in localized regions.

Characterization of GaAs and Si by a microwave photoconductance technique

Abstract: A nondestructive microwave photoconductance technique has been employed to investigate the uniformity of electrical transport properties in semi‐insulating, doped, or implanted GaAs. Although the measurement time is increased, the technique is also applicable to Si. A review of the advantages and limitations is discussed and some example applications to a variety of GaAs and Si structures are presented.

Hydrogen on Semiconductor Surfaces

Abstract: The state of understanding concerning hydrogen at semiconductor surfaces (external and internal) will be reviewed, the emphasis being on silicon and germanium. Topics will include hydrogen at crystalline-vacuum interfaces in ultra-high-vacuum systems, at grain boundaries in polycrystalline material, and at internal defect surfaces as arise in irradiated or ion-implanted material. The atomic configurations of hydrogen in semiconductors will be surveyed, including both monoatomic hydrogen [H] and molecular hydrogen [H2]. The diffusion coefficients and profiles associated with free [H] diffusion, trapping of [H] at defects, and formation of [H2] will be covered. The role of hydrogen in passivating defects will be discussed, as will the passivation mechanisms (bonding and non-bonding), and defect/surface reconstruction and chemically driven reconstruction.

Ohmic, superconducting, shallow AuGe/Nb contacts to GaAs

Abstract: An emerging new class of superconductor‐semiconductor devices requires Ohmic superconducting contacts which do not diffuse deeply into a semiconductor. We developed a contact to GaAs based on ∼150 A of AuGe covered with ∼2000 A of Nb annealed in reducing atmosphere at 390–420 °C for 1–5 s. The resulting contact has linear I‐V characteristics at all temperatures down to 4.2 K, resistivity of ∼2×10−6 Ω cm2 (∼0.1 Ω mm), and superconducting transition temperature Tc ≳8 K. Secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) studies revealed very shallow penetration of the active dopant Ge into GaAs; the upper limit for the thickness of the doped layer with Ge concentration over 1017 cm−3 is estimated as 200–300 A. Gold, a nonactive dopant (deep level) drops to below 1018 cm−3 within the same distance, with the possible tail extending further. Morphology and uniformity of a contact, as revealed in TEM and optical microscopy, is good, owing to the Nb overlayer which prevents AuGe fr...

Ultra-Thin p+ Layers in GaAs

Abstract: The formation of shallow (0.05–0.2 μm) p+ layers in GaAs by pulse diffusion of Zn from a doped oxide source, thermal diffusion of Cd by vapor transport, or by low energy implantation of Cd, Mg, Be, Zn or Hg ions was investigated by electrochemical capacitance-voltage profiling, Secondary Ion Mass Spectrometry, Rutherford backscattering and Hall measurements. Hole densities in excess of 1019 cm−3 are obtainable by either Zn diffusion or acceptor implantation, though the high temperature cycle must be kept to ≤3 sec at (≤1000°C to prevent excessive redistribution of the acceptor dopants. Pulse diffusion at temperature °C leads to shallow regions with atomic concentrations above 1019 cm−3, but electrically active concentrations orders of magnitude less. These results are explained in terms of the unavailability of a sufficient density of vacancies at low temperatures.

Deposition of Low-Stress Encapsulants on InP and GaAs

Abstract: AlN deposited by D.C. triode sputtering and spin-on, phosphorus-doped glass (PSG) layers on GaAs and InP were investigated as encapsulants. These films have similar expansion coefficients to both GaAs and InP, minimizing the amount of strain induced in the near-surface region of the underlying wafer. We have quantified this effect by direct measurements of the stress in the films and by using secondary ion mass spectrometry profiling to measure the redistribution of Cr and Fe in encapsulated GaAs and InP respectively during high temperature processing. The dopant redistribution is considerably less for the AlN and PSG films compared to the more conventional SiO 2 and Si 3 N 4 layers. The interaction of the films with the substrate at elevated temperatures is minimal as determined by Auger profiling and the electrical properties of the surface after removal of the encapsulants. The composition of the films remains essentially constant after annealing, as measured by Rutherford backscattering, and the thickness uniformity over large wafer diameters (2″) can be excellent with close control of the deposition parameters. The activation characteristics of low dose, Si-implanted layers in GaAs using either PSG or AlN are comparable to those obtained using capless annealing or SiO 2 or Si 3 N 4 encapsulation.