K. Rose

Interaction of High‐Intensity Laser Beams with Metals

The interaction of high‐intensity laser beams with metals has been analyzed on the basis of detailed quantitative measurements of the energy balance. The interaction of normal (not Q‐switched) pulses with energies ranging from 1 to 30 J from a Nd‐doped glass laser with metals having a variety of thermal and optical properties was studied. The time‐dependent radiation reflectance of the metals, measured during the laser pulse, is found to account for most of the incident power in the initial stages of the interaction. As time progresses, much of the incident power is absorbed. It was found that the greatest part of the absorbed radiation energy is used to remove material in the liquid and vapor phases. Due to a large heat of vaporization for most metals, the amount of energy required to remove a given mass is strongly dependent on the relative amounts removed in the liquid and vapor phases. To determine this ratio, the total mass of material and the mass of molten material were measured.

Enhanced‐Mode Radiation Detection by Superconducting Films

In the course of investigating radiant‐energy detection by high‐resistance superconducting films [≈10 KΩ/square (□)] an unexpected enhanced mode of detection was observed at microwave frequencies. This mode was observed in addition to and differed significantly from the expected thermal or bolometer mode of detection. Since that time detailed measurements have been made of the dependence of the enhanced‐mode response on bias current, incident power, temperature, and sample resistance; these are reported here. Correlation of the characteristics of the enhanced mode with the nonlinear VI (voltage‐current) characteristics of the film is shown. This suggests that the enhanced mode is the result of a nonlinear response to currents induced in the film by the incident radiation, which explains the short wavelength cutoff associated with the enhanced mode. Physical mechanisms which might cause this response are considered and fabrication techniques for these films are presented in detail. Since the initial report...

Radiant‐Energy Detection by Superconducting Films

Superconducting films offer promise as fast, sensitive detectors at intermediate frequencies from millimeter waves to near infrared. The superconductors marked temperature dependence of resistance about its transition temperature suggests that it would have a high responsivity as a bolometer, and operation at cryogenic temperatures suggests that a low NEP can be achieved. In addition, placing the sample in the liquid‐helium bath should result in very short response times (τ) on the order of 10 nsec. Films have been studied with sheet resistances from 200 Ω/sq to > 1000 Ω/sq. These films achieve NEP ≈ 10−9 W·Hz−1/2 as bolometers with τ≈20 nsec. There is an enhanced microwave response, NEP ≈ 10−11 W·Hz−1/2 with τ = 20 nsec, which is especially pronounced for high‐resistance films. This mode shows promise for use in the far‐infrared and submillimeter region. The bolometer mode compares favorably with other bolometers.

Avalanche Breakdown Effects in Near‐Intrinsic Silicon and Germanium

Impact ionization effects have been observed in near‐intrinsic silicon and germanium structures which exhibit an abrupt transition from a high‐resistance state to a low‐resistance state through a negative resistance region. Measurements on high‐resistivity n‐ and p‐type silicon samples with symmetric Ohmic or blocking contacts show that the threshold voltage for this transition is proportional to sample thickness which is indicative of bulk breakdown. On the other hand, the sustaining voltage in the low‐resistance state is thickness independent, indicating the formation of an avalanche breakdown layer. The results agree generally with Gunns theory of avalanche injection.

Electrical Properties of High‐Resistivity Nickel‐Doped Silicon

Detailed galvanomagnetic measurements on high‐purity, high‐resistivity nickel‐doped silicon confirm the existence of two acceptor levels lying 0.24±0.01 and 0.37±0.01 eV from the valence and conduction bands, respectively. The electron and hole mobilities are generally in good agreement from sample to sample. Hall mobilities have temperature variations of T−2.2 for electrons and T−3.2 for holes. The conductivity mobilities, obtained in regions of constant carrier concentration, are 1300(T/300)−2.2 for electrons and 500(T/300)−2.7 for holes. A significant degree of compensation was produced when nickel was diffused into both n‐ and p‐type material at elevated temperatures.

The temperature dependence of resistance in aggregate tin films

The temperature dependence of aggregate partially coalesced tin films can be explained by introducing an effective length‐to‐width ratio S which accounts for the mazelike structure of the film. The deviation of experiment from theory is less than 10% from 4 to 300 °K for films having room‐temperature sheet resistances of 5–660 Ω/square. The only adjustable parameters are S and the impurity resistivity ρI. The lattice resistivity of crystal tin, the experimentally determined film thickness, and diffuse surface scattering are used in the theory.

COMPARISON OF SUPERCONDUCTING AND SEMICONDUCTING BOLOMETERS.

Superconducting tin bolometers are now reasonably well understood, and the results of calculations of performance are given over a large range of sheet resistances (0.01–1000 Ω/□ at 4.2°K). Comparison of superconducting bolometers with semiconducting ones show that tin and germanium are equivalent in performance. The superconducting devices have the additional advantage of simplicity of sample preparation and lower impedance levels permitting higher operating speeds if desired.

SIMS analysis of low temperature ohmic contacts to GaAs

Abstract Secondary ion mass spectrometry (SIMS) is one of the most powerful techniques for the indepth characterization of materials. Inspite of the tremendous analytical potential of SIMS, one must be cognizant of artifacts induced by the ion beam. Such ion beam induced effects become even more important when one attempts to extract quantitative information from the depth profile. Of current interest is the ability to make good ohmic contacts to GaAs (i.e. AuGe/GaAs) with subsequent characterization of the interfacial structure. This study examines the ability of SIMS to accurately determine such structures in lieu of beam induced artifacts such as cascade mixing, preferential sputtering, and radiation-enhanced diffusion.

Electrical properties of laser annealed AuGe/GaAs ohmic contacts

Contact resistivity measurements of laser annealed AuGe/GaAs ohmic contacts as a function of depth (contact resistivity profiling) has shown a monotonically increasing contact resistivity profile for energy densities lower than 2.12 J/cm2. For energy densities higher than 2.12 J/cm2 a minimum in the profiles was observed at a depth of 1200 A. This suggests that minima previously observed in the variation of contact resistivity as a function of laser energy density are due to a surface phenomenon. These profiles further show that ohmic contacts can be made to GaAs by deposition of metal films on GaAs surfaces from which laser annealed AuGe films have been removed. Contact resistivities as low as 1×10−6 Ω cm2 were obtained even when metal was deposited on GaAs etched to a depth of 1000 A. Secondary ion mass spectroscopy profiles are included which allow the redistribution of Ge into GaAs to be compared with these contact resistivity profiles.