J. C. Hensel

Transistor action in Si/CoSi2/Si heterostructures

We report transistor action in a Si/CoSi2/Si structure. The thin silicide layer (<100 A), which acts as the base, is a single‐crystal metal, essentially continuous and locally exhibiting atomically perfect interfaces with Si. The transistor action is manifested by a common base current gain α as high as 0.6 and a voltage gain greater than 10.

Electrical transport properties of CoSi2 and NiSi2 thin films

Transport studies have been performed on thin films of CoSi2 and NiSi2 in the temperature range 1–300 K. The conductivities are metallic with essentially the same temperature dependence; however, the residual resistivities are markedly different even though the two silicides are structurally similar (the room‐temperature resistivity of NiSi2 being at least twice that of CoSi2 of 15 μΩ cm). The difference is attributed to intrinsic defects in NiSi2. This defect has been simulated by ion bombardment of the film where it is also shown that Matthiessen’s rule is obeyed over a remarkable range of bombardment doses.

Electrical and structural characterization of ultrathin epitaxial CoSi2 on Si(111)

We report the fabrication of epitaxial CoSi2 layers on Si(111) as thin as 1 nm. The crystalline lattice of these layers is coherent with the Si lattice, and the silicide is electrically continuous. There are pronounced structural differences between films which are less than 3 nm thick and those which are thicker. The resistivity of the layers increases sharply with decreasing thickness. This is the first report of the growth of coherent, electrically continuous CoSi2 layers on Si.

Operation of the Si/CoSi2/Si heterostructure transistor

A two‐current path model is presented to describe the operation of the Si/CoSi2/Si epitaxial, heterostructure transistor. The model gives a good account of the device behavior and allows us to conclude that it works by activated charge control, in a formal sense like a bipolar transistor. The analysis further suggests that with the fine base dimensions made possible by the single crystal, vertical structure one can foresee devices with β’s of a 100 or more, at the same time maintaining a transconductance close to the optimal value 0.04 mhos/mA characteristic of a charge injection device.

Dependence of the structural and electrical properties of ultrathin cobalt silicide films on formation conditions

We have studied the dependence of the electrical and structural properties of ultrathin cobalt silicide films on the annealing temperature and deposited Co thickness. If less than 10 A of Co is deposited, epitaxial type B CoSi 2 forms immediately. As the deposited thickness approaches 10 A, small amounts of Co 2 Si are observed. If greater than 10 A of Co is deposited, epitaxial Co 2 Si forms at room temperature, which proceeds either via the reaction Co 2 Si ⇉ CoSi ⇉ CoSi 2 or via Co 2 Si ⇉ CoSi 2 during annealing. In these thicker films our results suggest that the formation of type A CoSi 2 is correlated with the presence of Co 2 Si; the presence of CoSi as an intermediate phase is correlated with the occurrence of type B CoSi 2 . Both film thickness and reaction temperature strongly influence the electrical transport in these films such that very high resistivities are encountered when films either become very thin or are reacted at low temperatures. In the former case the size effect is responsible whereas in the latter the transport properties are dominated by extensive atomic-scale disorder.

Transport studies in single-crystal films of CoSi2 and NiSi2; A new class of quasi-two-dimensional metals

Measurements have been made of electrical transport in single-crystal, thin films of CoSi2 and NiSi2 controlled amounts of defects were introduced into certain films by 2 MeV 4He bombardment. These systems possess novel properties favorable for studies of quasi-two-dimensional phenomena in metals such as weak localization.

New Directions in the Growth of Epitaxial Insulators and Metals on Silicon

By nature of their high degree of crystalline perfection, epitaxial insulators and metals on semiconductors are structurally characterizable to a considerably greater extent than are polycrystalline or amorphous materials. This offers the possibility of correlating the detailed structure of these thin epitaxial films and their interfaces with their electrical properties. We have recently found evidence for the influence of the atomic structure of the CaF 2 /Si(ll1) interface on its electrical properties. Wehave also studied the structural and electrical properties of ultrathin epitaxial cobaltsilicide layers on Si(111).

Absorption of ballistic phonons by the 2D electron gas in A Si MOSFET

Abstract Experiments are described which measure absorption of ballistic phonons by the two-dimensional degenerate electron gas in the inversion layer of a (100)Si MOSFET; and the results are compared with theory.

Scattering and adsorption of ballistic phonons by the electron inversion layer in silicon: theory and experiment

This paper is a brief review of our investigations[1,2,3] using ballistic phonons to probe the two-dimensional electron gas (2DEG) in the inversion layer of Si. Our goal in the beginning was to elucidate the nature of the electron-phonon interaction for a 2DEG, an important problem physically just as in 3D but one rather less amenable to the conventional experimental procedures. In fact, in the absence of substantive results suspicions have arisen (mostly from interpretation of electrical transport) that the electron-phonon coupling in 2D might be anomalously strong compared to 3D[4]. Our ballistic phonon experiments are able to answer unequivocally that this is not the case.