R. C. Newman

Oxygen loss during thermal donor formation in Czochralski silicon: New insights into oxygen diffusion mechanisms

As‐grown Czochralski silicon samples with different oxygen concentrations have been heated at temperatures in the range 350–500 °C. Oxygen loss during anneals at low temperatures (T≤400 °C) is shown to follow second‐order kinetics and measurements led to values of oxygen diffusivity that were larger than normal by a factor of ∼3, assuming the capture radius for dimer formation was 5 A. Variations in the rate of [Oi] loss during more extended anneals could be explained if oxygen diffusion was initially enhanced but tended to its normal value as the anneals progressed. Much greater initial enhancements were derived from similar measurements for samples which had been hydrogenated by a heat treatment in H2 gas at 1300 °C for 30 min followed by a rapid quench to room temperature, and the enhancements were consistent with values derived from measurements of the relaxation of stress‐induced dichroism. At higher temperatures (T≥450 °C) the measured rates of [Oi] loss were less than the expected rate of Oi‐Oi int...

The lattice locations of silicon impurities in GaAs: effects due to stoichiometry, the Fermi energy, the solubility limit and DX behaviour

An outline of infrared localized vibrational mode absorption spectroscopy relevant to silicon impurities in GaAs is presented. Absorption lines from SiGa donors, SiAs acceptors, SiGa-SiAs pairs, SiGa-VGa (Ga vacancy) pairs and a complex Si-X (involving SiAs and VGa) have been identified as well as lines from SiGa-CuGa, SiGa-H, SiAs H and SiGa-BAs pairs. These observations are related to the electrical properties of n-type Bridgman, liquid-encapsulated Czochralski and molecular beam epitaxial (MBE) (001) GaAs, and to p-type liquid phase epitaxial and MBE (111)A layers. The discussion relates to dynamic site switching, effects due to counter-doping with shallow acceptors, the solubility of silicon, and DX behaviour observed in homogeneously doped material and proposed for delta -doped MBE (001) layers. The major problem is to understand the processes that limit the maximum carrier concentration that can be achieved in n-type crystals.

Effect of oxygen concentration on the kinetics of thermal donor formation in silicon at temperatures between 350 and 500 "C

Early measurements of the initial rate of thermal donor formation in Czochralski silicon at 450 °C revealed a dependency on the fourth power of the oxygen concentration. This result has led to the view that the core of the defects contained four oxygen atoms. We now show that this dependency is observed only for anneals close to 450 °C. Our results indicate that oxygen dimerization controls the thermal donor formation kinetics but that the dimers become increasingly unstable above 400 °C.

Hydrogen solubility in silicon and hydrogen defects present after quenching

Boron-doped silicon ((B) approximately 1017 cm-3) was heated in H2 gas at a temperature in the range 900<or=T<or=1300 degrees C and quenched to room temperature. Some of the dissolved hydrogen formed H-B pairs and the remainder (Hh), which was infrared inactive was released during anneals at T<or=200 degrees C leading to an increase in (H-B). The total hydrogen content, consistent with secondary-ion mass spectrometry, yielded a solubility given by SH=9.1*1021 exp(-1.80 eV/kT) cm-3. 2 MeV electron irradiation at room temperature converted Hh into defects incorporating two hydrogen atoms, suggesting that Hh may be present as H2 molecules.

Hydrogen-related shallow thermal donors in Czochralski silicon

Six shallow donors are shown to form in Czochralski silicon deliberately doped with hydrogen during the early stages of heat treatment at 350 degrees C. The ground state energies of five of these donors are altered slightly in material doped with deuterium rather than hydrogen, demonstrating the presence of hydrogen in their cores. One of the donors may account for some of the weak IR absorption features detected in as-grown material. The formation of these donors appears to be linked to the generation of the well known oxygen-related double thermal donors and may reflect the partial passivation of these latter defects.

Native defects in low‐temperature GaAs and the effect of hydrogenation

A range of experimental techniques has been used to measure point defect concentrations in GaAs layers grown at low temperatures (250 °C) by molecular‐beam epitaxy (LT‐GaAs). The effects of doping on these concentrations has been investigated by studying samples containing shallow acceptors (Be) or shallow donors (Si) in concentrations of ∼1019 cm−3. Material grown under As‐rich conditions and doped with Be was completely compensated and the simultaneous detection of As0Ga by near‐band‐edge infrared absorption and As+Ga by electron paramagnetic resonance confirmed that the Fermi level was near the midgap position and that compensation was partly related to AsGa defects. There was no evidence for the incorporation of VGa in this layer from positron annihilation measurements. For LT‐GaAs grown under As‐rich conditions and doped with Si, more than 80% of the donors were compensated and the detection of SiGa–VGa pairs by infrared localized vibrational mode (LVM) spectroscopy indicated that compensating VGa de...

Solubility of hydrogen in silicon at 1300 °C

The incorporation of hydrogen in boron doped Czochralski silicon heated to 1300 °C in H2 gas has been studied. The anneal was terminated by a rapid quench to room temperature giving rise to an unknown hydrogen‐related defect as well as H‐B close pairs. All the hydrogen in the crystal can be driven into such pairs by a low temperature (200 °C) anneal, after which the values of [H‐B] [D‐B] are in agreement with the total deuterium concentration, measured by secondary ion mass spectrometry. The estimated solubility of 1.5×1016 cm−3 is not affected by the isotopic mass of the hydrogen nor by the presence of boron or oxygen impurities.

Shallow Thermal Donors in Silicon: The Roles of Al, H, N, and Point Defects

Three families of shallow thermal donors have been identified in annealed Czochralski silicon from measurements of their infrared electronic transitions using Fourier transform spectroscopy. Donors produced in Al-doped Si incorporate an Al impurity; centers produced in hydrogenated material contain an H (or D) atom; a third set of donors labeled STD(X)N produced in nitridated or irradiated pre-hydrogenated samples may incorporate a lattice vacancy rather than a nitrogen atom. A critical review of the literature is made and some rationalization has been effected. Comments are included about the formation of donor centers following anneals of heavily damaged float-zone Si that also contains hydrogen.

Thermal donor formation and annihilation at temperatures above 500 °C in Czochralski-grown Si

Thermal donors (TDs) are generated in Czochralski (CZ)-grown silicon by heat treatments around 450 °C. They form several individual effective-mass-like donors with slightly different ionization energies and act as double donors (TDx0,TDx+). Heat treatments at elevated temperatures (e.g., >500 °C) lead to a competition of the formation and the annihilation of TDs. We studied the formation and the annihilation of TDs in the temperature range between 520 and 700 °C. CZ-grown Si samples with an initial total TD concentration of ∼5×1015 cm−3 were employed to study the annihilation of TDs. The number of interstitial oxygen atoms generated per annihilated TD center depends on the temperature and ranges from 4 to 24. For the temperature range investigated the activation energy for thermal annihilation of TDs was determined to be 2.5±0.4 eV. The same CZ-Si material but with an initial TD concentration of ∼2×1013 cm−3 was used to study the formation of TDs. During annealing, the concentrations of individual TDs rea...

Carbon acceptors passivated with hydrogen and the search for carbon donors in highly doped GaAs:C

Highly carbon doped p-type GaAs grown by MOVPE shows infrared absorption lines from localized vibrational modes of CAs acceptors and passivated H-CAs pairs. A comparison with samples grown by MOMBE shows that an unassigned line at 563 cm-1 is due to a mode of H-CAs pairs, although an isotopic analogue from D-CAs pairs in plasma-treated samples has not been detected. The important new result is the demonstration that the line cannot be due to CGa donors, and so there is still no evidence for the amphoteric behaviour of carbon impurities in GaAs.