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Germanium is a widely used material for electronic and optoelectronic devices and recently it has become an important material for spintronics and quantum computing applications. Donor spins in silicon have been shown to support very long coherence times (T2) when the host material is isotopically enriched to remove any magnetic nuclei. Germanium also has nonmagnetic isotopes so it is expected to support long T2's while offering some new properties. Compared to Si, Ge has a strong spin-orbit coupling, large electron wave function, high mobility, and highly anisotropic conduction band valleys which will all give rise to new physics. In this Letter, the first pulsed electron spin resonance measurements of T2 and the spinlattice relaxation (T1) times for 75As and 31P donors in natural and isotopically enriched germanium are presented. We compare samples with various levels of isotopic enrichment and find that spectral diffusion due to 73Ge nuclear spins limits the coherence in samples with significant amounts of 73Ge. For the most highly enriched samples, we find that T1 limits T2 to T2 = 2T1. We report an anisotropy in T1 and the ensemble linewidths for magnetic fields oriented along different crystal axes but do not resolve any angular dependence to the spectral-diffusion-limited T2 in samples with 73Ge. [ABSTRACT FROM AUTHOR]

We present an electron spin resonance (ESR) approach to characterize shallow electron trapping in band-tail states at Si/SiO2 interfaces in metal-oxide-semiconductor (MOS) devices and demonstrate it on two MOS devices fabricated at different laboratories. Despite displaying similar low temperature (4.2 K) peak mobilities, our ESR data reveal a significant difference in the Si/SiO2 interface quality of these two devices, specifically an order of magnitude difference in the number of shallow trapped charges at the Si/SiO2 interfaces. Thus, our ESR method allows a quantitative evaluation of the Si/SiO2 interface quality at low electron densities, where conventional mobility measurements are not possible. [ABSTRACT FROM AUTHOR]

We have investigated the influence of Si–N complexes on the electronic properties of GaAsN alloys. The presence of Si–N complexes is suggested by a decrease in carrier concentration, n, with increasing N-composition, observed in GaAsN:Si films but not in modulation-doped heterostructures. In addition, for GaAsN:Te (GaAsN:Si), n increases substantially (minimally) with annealing-T, suggesting a competition between annealing-induced Si–N complex formation and a reduced concentration of N-related traps. Since Si–N complex formation is enhanced for GaAsN:Si growth with the (2×4) reconstruction, which has limited group V sites for As–N exchange, the (Si–N)As interstitial pair is identified as the dominant Si–N complex. [ABSTRACT FROM AUTHOR]

We have used rapid thermal annealing to investigate the influence of N interstitials on the electronic properties of GaAsN alloys. Nuclear reaction analysis reveals an annealing-induced decrease in the interstitial N concentration, while the total N composition remains constant. Corresponding signatures for the reduced interstitial N concentration are apparent in Raman spectra. Following annealing, both the room-T carrier concentration, n, and the mobility increase. At higher measurement-Ts, a thermally activated increase in n suggests the presence of a trap near GaAsN conduction band edge with activation energy 85±15 meV. The annealing-induced increase in n suggests the association of the trap with interstitial N. [ABSTRACT FROM AUTHOR]

We examine the role of N environment on persistent photoconductivity (PPC) in GaAs1-xNx films. For x > 0.006, significant PPC is observed at cryogenic temperatures, with the PPC magnitude increasing with increasing x due to an increase in the density of N-induced levels. Interestingly, rapid thermal annealing suppresses the PPC magnitude and reduces the N interstitial fraction; thus, the N-induced level is likely associated with N interstitials. PPC is attributed to the photogeneration of carriers from N-induced levels to the conduction-band edge, leading to a modified N molecular bond configuration. With the addition of thermal energy, the ground state configuration is restored; the N-induced level is then able to accept carriers and the conductivity decays to its preillumination value. [ABSTRACT FROM AUTHOR]