Michael Stavola

Diffusivity of oxygen in silicon at the donor formation temperature

We present data on oxygen diffusivity in silicon for the temperature range 270–400 °C. The diffusivity is determined from the recovery kinetics of a stress induced dichroism in the 9‐μm oxygen infrared absorption band. We combine our data for well dispersed oxygen (i.e., crystals heat treated at 1350 °C for 20 h), with Mikkelsen’s recent mass transport work at higher temperature to obtain the diffusivity, D=0.17 exp (−2.54/kT), for the range 330–1240 °C. We have also found that the oxygen atomic hopping times can be as much as 100 times faster in crystals that have not received the 1350 °C heat treatment.

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

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 w...

Passivation of Si donors and DX centers in AlGaAs by hydrogen plasma exposure

The effect of hydrogen plasma exposure upon shallow donors and DX centers in silicon‐doped AlGaAs has been investigated by deep level transient spectroscopy and capacitance versus voltage measurements. Following exposure to a hydrogen plasma for 30 min at 250 °C, the shallow level and DX center activity are reduced by an order of magnitude throughout a 1.6‐μm‐thick layer of molecular beam epitaxially grown AlGaAs. Isochronal annealing studies showed that both the shallow donor and DX center electrical activity recover together at about 400 °C. The shallow donor recovery mimics the behavior of donors in GaAs and has an activation energy of 2.0 eV. The DX center recovery shows a distribution of activation energies centered at 2.1 eV with a full width at half‐maximum of 0.25 eV. The hydrogen passivation chemistry of DX centers and shallow donors support models in which isolated Si impurities give rise to both DX behavior and shallow levels.

Hydrogen passivation of acceptors in p‐InP

The problem of hydrogenation of InP without surface degradation has been surmounted by exposure of the InP surface to a hydrogen plasma through a thin SiNx(H) cap layer. This layer is H permeable at the hydrogenation temperature of 250 °C, but P or PH3 impermeable thus minimizing PH3 loss and the attendant In droplet formation. In contrast to our results for this type of plasma exposure of GaAs, we find that shallow acceptors in InP are heavily passivated, whereas shallow donors are only very weakly affected. For example, p+‐InP(Zn) of 3×1018 cm−3 has its residual hole concentration reduced to ≤3×1014 cm−3 over a depth of 1.3 μm by a 250 °C, 0.5 h deuteration. The presence of acceptors impedes H (or D) indiffusion, as indicated by D diffusion under the same conditions occurring to depths of 18 and 35 μm in p‐InP (Zn, 2×1016 cm−3) and n‐InP (S or Sn), respectively. Annealing for 1 min at 350 °C causes the acceptor passivation to be lost and the hole concentration to be returned to its prehydrogenation leve...

Vibrational characteristics of acceptor‐hydrogen complexes in silicon

Acceptor‐hydrogen complexes for the group III acceptors, B, Al, and Ga, in Si have been studied with low‐temperature infrared spectroscopy. The Si‐H stretching band narrows dramatically upon cooling to low temperature thereby aiding the detection of the vibrations of the Al and Ga acceptor‐H complexes. The frequency 2201 cm−1 we have measured for the Al‐H complex is in reasonable agreement with the prediction made by G. G. DeLeo and W. B. Fowler [Phys. Rev. B 31, 6861 (1985)] (2220 cm−1 for a 〈111〉 interstitial configuration for the H). Assignment of the new vibrational bands is confirmed by isotopic substitution. The strength of the absorption provides evidence that the passivation is not the result of compensation alone and that a major fraction of the passivated acceptors result in acceptor‐H complexes. A new, low‐energy excitation of the acceptor‐hydrogen complexes gives rise to a sideband to the main stretching vibration and explains the pronounced energy shift and narrowing of the spectra upon cooli...

Hydrogenation of GaAs on Si: Effects on diode reverse leakage current

Plasma hydrogenation for 3 h at 250 °C of GaAs layers grown directly on Si substrates by metalorganic chemical vapor deposition, followed by a 5‐min, 400 °C anneal to restore the passivated shallow donor electrical activity, increases the reverse breakdown voltage of Schottky diode structures from 2.5 to 6.5 V. This improvement appears to be a result of the passivation by atomic hydrogen of defects such as threading dislocations caused by the large (4%) lattice mismatch between GaAs and Si. A reduced Schottky barrier height is exhibited by hydrogenated samples, consistent with As depletion of the surface occurring during the long duration plasma processing.

Infrared spectrum of interstitial oxygen in silicon

A stress‐induced dichroism study of the 1106‐cm−1 and 515‐cm−1 modes of interstitial oxygen in silicon has been undertaken in order to assign the 515‐cm−1 mode. It has been found that the 515‐cm−1 mode is due to the symmetric stretching motion of the Si–O–Si ‘‘defect molecule’’ that has often been used to explain the vibrational spectrum of interstitial oxygen. The implications of the assignment to both the structure of the oxygen interstitial and to the characterization of oxygen concentration are discussed.

Thickness dependence of material quality in GaAs-on-Si grown by metalorganic chemical vapor deposition

The evolution with increasing layer thickness of the structural and electrical properties of GaAs grown directly on Si or Si‐on‐insulator (SOI) by metalorganic chemical vapor deposition is reported. There is a substantial improvement in the surface morphology and near‐surface crystallinity of the GaAs in thicker films (≥1.5 μm). The implant activation efficiency of 60‐keV 29Si ions at a thickness of 4 μm is comparable to that seen in bulk GaAs. The deep level concentration is also observed to decrease with increasing layer thickness. Transmission electron microscopy reveals average defect densities near 108 cm−2 in films deposited either on misoriented or exact (100) Si, and in those grown on SOI.

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

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.

The oxygen related donor effect in silicon

Abstract Current and capacitance transient spectroscopies have been applied to heat treated silicon. Two oxygen related, donor states, E(0.07) and E(0.15), introduced during heat treatment at 450°C, were identified. The production of these states is not enhanced by the presence of presence of point, lattice defects introduced by 1 MeV electron bombardment. New measurements of the diffusivity of interstitial oxygen between 270–400°C were made employing the recovery of a stress-induced dichroism of the 9 μm absorption band. For well dispersed oxygen, the same oxygen transport mechanism is operative over the range of 270–1250°C. However, prior heat treatment at 900°C yields a factor of 100 enhancement in the low temperature jump rate. These observations are found consistent with donor formation resulting from an oxygen aggregation reaction.