R. E. Pritchard

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...

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.

Shallow thermal donors associated with H, Al and N in annealed Czochralski silicon distinguished by infrared spectroscopy

Electronic transitions of shallow thermal donors (STDs) in aluminium-doped Czochralski (CZ) Si annealed at C have different energies from those of STDs observed in annealed, hydrogenated boron-doped CZ Si. A third type of STD is observed in boron-doped Si pre-heated in nitrogen gas and annealed at C. Combinations of the three types of STDs can be observed in suitably treated samples. The incorporation of H and Al in STDs has been supported by electron - nuclear double-resonance measurements of the Si-NL10 electron paramagnetic resonance spectrum but the incorporation of nitrogen remains uncertain.

H2 molecules in crystalline silicon

Abstract Infrared spectra from low-doped, hydrogenated silicon have revealed very weak absorption from hydrogen molecules. In Czochralski silicon, vibrational modes from molecules paired with interstitial oxygen atoms (OiH2) have been identified, together with a vibrational mode (ν3HH) from molecules trapped at a second site. A low temperature annealing study (T

The bonding of CAs acceptors in InxGa1-xAs grown by chemical beam epitaxy using carbon tetrabromide as the source of carbon

InxGa1−xAs layers (0≤x≤0.37) doped with carbon (>1020 cm−3) were grown on semi‐insulating GaAs substrates by chemical beam epitaxy using carbon tetrabromide (CBr4) as the dopant source. Hall measurements imply that all of the carbon was present as CAs for values of x up to 0.15. The C acceptors were passivated by exposing samples to a radio frequency hydrogen plasma for periods of up to 6 h. The nearest‐neighbor bonding configurations of CAs were investigated by studying the nondegenerate antisymmetric hydrogen stretch mode (A−1 symmetry) and the symmetric XH mode (A+1 symmetry) of the H–CAs pairs using IR absorption and Raman scattering, respectively. Observed modes at 2635 and 450 cm−1 had been assigned to passivated Ga4CAs clusters. New modes at 2550 and 430 cm−1 increased in strength with increasing values of x and are assigned to passivated InGa3CAs clusters. These results were compared with ab initio local density functional theory. Modes due to AlInGaCAs clusters were detected in samples containing...