W. C. Dautremont‐Smith

Anisotropic etching of SiO2 in low‐frequency CF4/O2 and NF3/Ar plasmas

Anisotropic etching of SiO2 films is reported in low frequency (∼100 kHz), moderate‐pressure (0.35 Torr) CF4/O2 and NF3/Ar plasmas. Rates up to 2000 A/min were achieved with high selectivity over GaAs and InP substrates. The etching mechanism was studied with optical spectroscopy and downstream chemical titrations. Anisotropy is attributed to ion‐enhanced reactivity of fluorine atoms with SiO2 at rates up to two hundred times larger than purely chemical etching by fluorine atoms. Damage and product sputter desorption models of this process were evaluated. These two models are nearly mathematically equivalent at steady state, and show that the effectiveness of ions in etching by enhanced reaction is roughly 15 times that in physical sputtering under these conditions.

Hydrogenation of shallow‐donor levels in GaAs

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

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...

Damage to InP and InGaAsP surfaces resulting from CH4/H2 reactive ion etching

Structural and electrical damage imparted to InP and In0.72Ga0.28As0.6P0.4 (λg≂1.3 μm) surfaces during CH4/H2 reactive ion etching (RIE) have been examined. X‐ray photoelectron spectroscopy was used to monitor changes in the surface chemistry, Rutherford backscattering spectrometry was used to measure crystallographic damage, and current‐voltage and capacitance‐voltage measurements were made to examine electrically active damage and its depth. Two classes of damage are observed: crystallographic damage originating from preferential loss of P (As) and/or ion bombardment‐induced collision cascade mixing and, for p‐type material, hydrogen passivation of Zn acceptors. Etching at 13.6 MHz, 60–90 mTorr, 10% CH4/H2, and bias voltages of ∼300 V contains gross (≳1%) damage as measured by RBS to within 40 A and electrically active damage to within 200 A of the surface. This is a factor of 3–6 shallower than other RIE processes operated below 10 mT with comparable or higher bias voltages. Acceptor passivation of bot...

Passivation of acceptors in InP resulting from CH4/H2 reactive ion etching

Reactive ion etching of InP with CH4/H2 mixtures leads to hydrogen passivation of near‐surface Zn acceptors but not S donors. Secondary‐ion mass spectrometry (SIMS) measurements of CH4/D2 etched samples show deuterium diffuses to a depth of 2000 A in p‐InP (1.5×1018 cm−3) when etching at a rate of 520 A/min and a temperature of about 80 °C. Acceptor passivation occurs to the same depth. For n‐InP, no donor passivation is observed, even though SIMS shows deuterium diffusion to a depth of 7000 A. Annealing at 350 °C for 1 min restores carrier concentrations to near pre‐etched levels.

Electrochromic iridium oxide films prepared by reactive sputtering

We report the preparation and electrochromic properties of iridium oxide films deposited by reactively sputtering iridium in a humidified oxygen discharge. These sputtered iridium oxide films (SIROFs) have the fast coloring and bleaching kinetics and excellent stability previously observed for anodically grown iridium oxide films (AIROFs). SIROFs deposited on SnO2‐coated glass can be modulated from clear to blue‐gray with properties similar to those of AIROFs. In addition, SIROFs deposited on metal substrates exhibit a variety of colors which can be electrically altered. This adds a new dimension to the range of potential applications for iridium oxide displays.

Pt/Ti/p‐In0.53Ga0.47As low‐resistance nonalloyed ohmic contact formed by rapid thermal processing

Very low resistance nonalloyed ohmic contacts of Pt/Ti to 1.5×1019 cm−3 Zn‐doped In0.53Ga0.47As have been formed by rapid thermal processing. These contacts were ohmic as deposited with a specific contact resistance value of 3.0×10−4 Ω cm2. Cross‐sectional transmission electron microscopy showed a very limited interfacial reacted layer (20 nm thick) between the Ti and the InGaAs as a result of heating at 450 °C for 30 s. The interfacial layer contained mostly InAs and a small portion of other five binary phases. Heating at 500 °C or higher temperatures resulted in an extensive interaction and degradation of the contact. The contact formed at 450 °C, 30 s exhibited tensile stress of 5.6×109 dyne cm−2 at the Ti/Pt bilayer, but the metal adhesion remained strong. Rapid thermal processing at 450 °C for 30 s decreased the specific contact resistance to a minimum with an extremely low value of 3.4×10−8 Ω cm2 (0.08 Ω mm), which is very close to the theoretical prediction.