R.E.M. Vickers

Strong terahertz emission from (100) p-type InAs

Terahertz emission has been observed from (100) Zn-acceptor-doped InAs under illumination by fs pulses of near-infrared radiation. Turning the crystal about the surface normal produces two maxima per rotation, whether the angle of incidence is 45° or 75°, in contrast to (111) p-InAs, where three maxima per rotation have been reported. The emitted terahertz power has a quadratic variation with the pump power and decreases with increasing temperature in the range 20–300K. This behavior is consistent with a photocurrent surge being the dominant terahertz generating mechanism at low excitation fluences. The p-type InAs generates about two orders of magnitude more power than the standard unbiased terahertz emitter, 1mm thick ZnTe.

Zeeman and Piezo-Zeeman spectroscopy of acceptors in germanium

Abstract A brief review is given of the Zeeman and piezo-Zeeman results for the spectra of shallow acceptors in germanium. Also included are new data for the Zeeman spectra of thallium with B ∥〈100〉 and boron, gallium and thallium under B ∥〈111〉. The observations are for field strengths up to 7T and the results compared with recent calculations of these effects. New data for neutral zinc in germanium with B ∥〈100〉 is also indicated.

Comparison of photoexcited p-InAs THz radiation source with conventional thermal radiation sources

P-type InAs excited by ultrashort optical pulses has been shown to be a strong emitter of terahertz radiation. In a direct comparison between a p-InAs emitter and conventional thermal radiation sources, we demonstrate that under typical excitation conditions p-InAs produces more radiation below 1.2 THz than a globar. By treating the globar as a blackbody emitter we calibrate a silicon bolometer which is used to determine the power of the p-InAs emitter. The emitted terahertz power was found to be 98±10 nW in this experiment.

Terahertz emission from (100)p-InAs

Terahertz emission from (100) p-type InAs illuminated by ultrafast near-infrared pulses is investigated. A two-fold rotational symmetry was observed when rotated about the surface normal. A quadratic relationship was found for the emission dependence on optical pump power. These suggest the presence of photocarrier transport and optical rectification mechanisms. The InAs emission was found to exceed that of a blackbody radiator for frequencies below 1 THz for nominal input power levels. The generated power was found to be roughly two orders of magnitude greater than a 1mm ZnTe emitter.

Bulk stress due to surface damage of crystalline silicon and germanium

It is found that abrading two opposing surfaces of either crystalline Si or Ge samples results in homogeneous, uniaxial stress throughout the bulk perpendicular to the damaged surfaces. The latter are chosen to coincide with simple crystallographic planes. This conclusion is reached by analyzing the splittings, intensities, and polarizations of the absorption lines of the Lyman series of bulk shallow impurities in the abraded semiconductors. This effect has been observed for samples which range in thickness, t, from 1 to 3 mm, the internal stress being proportional to t−1.It is found that abrading two opposing surfaces of either crystalline Si or Ge samples results in homogeneous, uniaxial stress throughout the bulk perpendicular to the damaged surfaces. The latter are chosen to coincide with simple crystallographic planes. This conclusion is reached by analyzing the splittings, intensities, and polarizations of the absorption lines of the Lyman series of bulk shallow impurities in the abraded semiconductors. This effect has been observed for samples which range in thickness, t, from 1 to 3 mm, the internal stress being proportional to t−1.

Spherical, cylindrical and tetrahedral symmetries; hydrogenic states at high magnetic field in Si:P

Phosphorous donors in silicon have an electronic structure that mimics the hydrogen atom, albeit on a larger length, smaller energy and smaller magnetic field scale. While the hydrogen atom is spherically symmetric, an applied magnetic field imposes cylindrical symmetry, and the solid-state analogue involves, in addition, the symmetry of the Si crystal. For one magnetic field direction, all six conduction-band valleys of Si:P become equivalent. New experimental data to high laboratory fields (30 T), supported by new calculations, demonstrate that this high symmetry field orientation allows the most direct comparison with free hydrogen.

ANOMALIES AND ZEEMAN SPECTRA OF THE LYMAN SERIES OF NEUTRAL ZINC IN GERMANIUM

A doublet observed for the G line of Zn(0) without applied perturbation is attributed to relative shifts of the two Γ−4 states which are part of the compound excited state of this transition. This effect also increases the energy spacing between the G doublet and the rest of the lines of the Lyman series. The energies and widths of all the lines are temperature dependent at temperatures where group III lines no longer show these effects. Zeeman measurements have demonstrated conclusively that the low temperature Lyman series of Zn(0) in Ge arises from the 1Γ+1 ground state. These studies also establish that the Zeeman excited states of Zn(0) are compounded from wave functions identical to those of the ground state of Zn− and the excited states of group III acceptors in Ge.

Piezo-spectroscopy of the C line of gallium in germanium

Abstract Experimental results are presented on the behaviour of the C line of gallium impurity in germanium under uniaxial compression along a 〈100〉 direction. The C line stress spectrum is found to have ten components arising from the splitting of a complex final state consisting of the closely spaced combination: 1Γ - 7 +3Γ - 8 +3Γ + 8 . The participation of the even parity state in the C transition has not been previously reported. Recent theoretical calculations are shown to give splitting values in good agreement with these results.

Zeeman spectroscopy of ZnH complex in germanium

Abstract The Zeeman spectra of the complex ZnH in Ge have been studied for B |〈100〉 and 〈111〉. The excited state of the D line exhibits a splitting which is identical to that of the D line of the group III acceptors. The results for the ground state conform to the model developed for this defect which requires that its axis be along any one of the four 〈111〉 covalent bond directions of the host.

Zeeman spectroscopy of neutral copper in germanium

Abstract The results of high field Zeeman spectroscopy of the D line of neutral copper (Cu(0)) acceptors in Ge are presented. It is found that the excited state of this transition has a splitting which is identical to that observed for this same transition for group III impurities, demonstrating that the excited state for Cu(0) is the product state whose symmetry is 1Γ1+ × 2Γ8− of O h . Similar results are obtained for the G line. The ground state g-factors have the values −0.04±0.01 and +0.30±0.01 for g′1 and g′2, respectively.