Notes: The interfacial interactions between (HgCd)Te and Ti, an ultrareactive metal, have been examined using photoelectron spectroscopy with synchrotron radiation. Deposition of small quantities of Ti, which form tellurides that are thermodynamically more stable than HgTe or CdTe, causes a loss of both Hg and Cd from the interface. The rate of Hg depletion is greater than that of Cd and is greater than the rate of Hg depletion yet observed for any other overlayer metal. This greater Hg loss is attributed to the increased disruption of the semiconductor surface region caused by the loss of Cd. Unlike the cases of Al and In, but similar to that of Cr, no additional band bending is observing during the early stages of metal deposition.

Notes: The resistance and 1/f noise of Au and Al contacts to ion-sputtered p-type Hg0.79Cd0.21Te and of Ge contacts to Hg0.7Cd0.3Te have been measured at temperatures of 12, 40, 77, and 295 K. The Au and Al contacts were ohmic at all temperatures whereas the Ge contacts were partially rectifying. The specific contact resistance for Au and Al varied by about a factor of 10 up to 9×10−4 Ω cm2 and 3×10−3 Ω cm2, respectively, at 295 K, and there was little variation in resistance down to 12 K. The 1/f noise of the Au and Al contacts could be described as a power spectral density of resistance fluctuations SR which varied with the contact diameter d as SR∝d−m, where 5≤m≤6 for Au and 2≤m≤3 for Al. The values of m suggest that whereas the 1/f noise of the Au contacts originated at the Au/(Hg,Cd)Te interface or in the underlying (Hg,Cd)Te, the 1/f noise of the Al contacts originated in a surface conduction layer next to the contact. The magnitude of the 1/f noise was significantly larger than expected for any fundamental 1/f noise source.

Notes: A novel technique is presented for interpreting magnetic field-dependent Hall data at magnetic fields below the range at which Shubnikov–de Haas oscillations occur. The technique generates a "mobility spectrum'' in which the maximum carrier density or maximum conductivity is determined as a continuous function of mobility. Examples of the use of the technique with synthetic data as well as data from HgCdTe and GaAs/AlGaAs samples are provided. Other uses of the procedure, including measurement of Fermi surface shapes and direct measurement of the distribution of relaxation times, are discussed.

Notes: The interactions of the reactive metals Al and In with both cleaved and sputtered p-type Hg1−xCdxTe surfaces have been investigated using synchrotron radiation-induced ultraviolet photoelectron spectroscopy. The sputtered surfaces are depleted of a fraction of their Hg (∼25% and ∼40% for x=0.21 and x=0.28 material, respectively, relative to the Hg found on the corresponding cleaved surfaces) and are more inverted than the cleaved surfaces with the Fermi level higher in the conduction band. During metal deposition, the cleaved and sputtered surfaces behave similarly: in the initial stages, the metal reacts with the HgTe alloy component to form a metal telluride and Hg, which leaves the surface region. At the same time, the inverted surface becomes more degenerate. After the metal has reacted with all the available HgTe within a certain surface region, an unreacted metallic film grows on the surface. Such identical behavior of the two types of surfaces is explained by the large difference in thermodynamic stability between HgTe and the metal tellurides.

Notes: The interaction between thin layers of Au and both cleaved and sputtered p-type Hg0.72Cd0.28Te and sputtered p-type Hg0.79Cd0.21Te surfaces has been investigated with ultraviolet photoelectron spectroscopy using synchrotron radiation. Only a small loss of Hg from the interface was observed during Au deposition, in contrast to that seen during Al and In deposition reported elsewhere. The retention of Hg is explained by the lower stability of AuTe2 compared with HgTe, which makes the exchange reaction between Au and Hg unfavorable. Small differences in the Hg/Cd ratio following Au deposition with different surface preparations and material were noted. They were attributed to reduced stability of the ion-bombarded surface caused by sputter-induced defects and reduced strength of the Hg–Te bond, which resulted from the increased local CdTe concentration. Although Au diffused into the semiconductor to partially compensate for the cleavage-induced defects (which act as donors), it was not able to compensate appreciably for the larger number of sputter-induced defects.

Notes: Recent measurements of less-than-full shot noise in GaAs/AlGaAs quantum-well infrared detectors can be explained in terms of standard photoconductor generation-recombination theory. Therefore, more complex models are not yet necessary.

Notes: The photoconductive gain, g, and generation-recombination (GR) noise of multiple-quantum-well infrared detectors are calculated for structures in which the well capture probability, pc, and the fraction of current derived from tunneling are allowed to vary through the structure. For uniform pc and no tunneling current, g=1/(Npc), where N is the number of wells. The GR noise power under the same conditions is 4eI¯gB(1−pc/2), where e is electronic charge, I¯ is the mean current, and B is the measurement bandwidth. When pc(very-much-less-than)1, the noise contributions from carrier generation and decay (recombination) are equal as in a homogeneous photoconductor. However, when pc→1, the recombination noise decreases to zero, and the noise is equal to the shot noise of N series-connected, independent junctions.

Notes: Abstract The semiclassical approach to modeling atomic collision systems lies between the easy classical model, which is most useful for simple systems in which quantum effects can be neglected, and the full quantum mechanical description, which is generally too difficult for more than simple systems. By adding a mathematical model of quantum-mechanical effects to a classical Hamiltonian, the calculational simplicity of the manybodied classical model can be extended to the quantum realm; the validity of this approach can be measured by the degree to which the semiclassical model can replicate experimental data. Evolving from earlier work by Kirschbaum and Wilets, our model uses momentum-dependent pseudopotentials to exclude particles from quantum mechanically forbidden regions of phase space: a Heisenberg pseudopotential stabilizes the system by preventing atomic electrons from collapsing into the nucleus, while a Pauli pseudopotential holds identical electrons apart in phase space, structuring the electron configuration. This semiclassical model of an atom is then used as a target in collision simulations with a heavy projectile, which is itself treated classically. Collision cross sections are calculated from a series of simulation runs with Monte Carlo target orientations and impact parameters. The model is dialed in to match published experimental proton stopping powers, then applied to other systems of interest. Here, we present stopping and capture cross sections for antiprotons colliding with our semiclassical model of He. Antiproton stopping on He is compared with the results reported recently by the OBELIX group, and initial capture states are discussed in some detail, including a comparison with the quantum-mechanical calculations originally presented by Yamazaki and Ohtsuki and the later paper by Shimamura; among the differences: (1) In our calculations, the angular momentum of captured antiprotons obeys the classical limit l=n, and (2) the angular momentum distribution of our $$He^ + \bar p$$ states extends beyond that of the quantum calculations. It should be emphasized that our calculations are for times much shorter than the metastable lifetimes.