K. A. Harris

CdTe metal‐semiconductor field‐effect transistors

We report the first demonstration of CdTe metal‐semiconductor field‐effect transistors. These transistors were fabricated using n‐type CdTe films grown by photoassisted molecular beam epitaxy. Using this new film deposition technique, it is possible to obtain highly activated n‐type or p‐type films suitable for device applications. In the present work, transistor structures with 5 or 100 μm gate lengths having channel dopings in the range from 2×1016 to 2×1017 cm−3 were fabricated and tested. The 5 μm gate devices have transconductances as large as 10 mS/mm and pinch‐off voltages of 4.0 V.

Characterization study of a HgTe‐CdTe superlattice by means of transmission electron microscopy and infrared photoluminescence

We report the first transmission electron microscopy (TEM) study of a HgTe‐CdTe superlattice. The superlattice consists of 250 layer pairs of HgTe‐CdTe on a (100) CdTe substrate and was grown at 175 °C by molecular beam epitaxy. Vertical cross‐section TEM images show a highly regular structure of the superlattice from the CdTe substrate to the free surface, indicating that interdiffusion effects at interfaces are minimal. Diffraction patterns taken from the first 30 pairs of layers of the superlattice from the CdTe buffer layer show a series of satellite spots up to the sixth order. This implies that the interfacial sharpness of this HgTe‐CdTe superlattice is comparable to those interfaces of high quality III‐V semiconductor superlattices. The HgTe‐CdTe superlattice exhibits an infrared photoluminescence peak at 357 meV, in reasonable agreement with theoretical predictions of its band gap.

Far‐infrared study of alloying in the HgTe‐CdTe superlattice

The far‐infrared reflectivity spectra of three HgTe‐CdTe superlattices from two sources [HgTe/CdTe thicknesses (A/A): 64/26, 7/35, 32/57] have been measured at 300, 77, and 6 K. Analysis of transverse optical phonon structure between 80 and 180 cm−1 with different alloying models shows that the first of these superlattices contains HgTe and CdTe with no evidence of significant mixing, whereas the others contain HgTe and homogeneous Hg1−xCdxTe. An earlier study of the HgTe‐CdTe band gap also indicated homogeneous alloying. The reflectivity data were analyzed with a superlattice dielectric function which is shown to be valid in the far infrared.

Properties of doped II–VI films and superlattices grown by photoassisted molecular beam epitaxy

Abstract A new film growth technique, photoassisted molecular beam epitaxy (PAMBE), has been used to prepare substitutionally doped II–VI semiconductor compounds. This epitaxial growth technique differs from conventional MBE in that the substrate is illuminated during the entire film growth process. We have used this new technique to prepare conducting layers of CdTe and CdMnTe. In our experiments, the output from an argon ion laser is used as the source of illumination. In and Sb were employed as n-type and p-type dopants, respectively. Conducting n-type CdMnTe: In-CdTe superlattices have also been grown along with doped CdMnTe: Sb-CdTe structures. The structural, electrical, and optical properties of the conducting epilayers were investigated by means of double crystal X-ray diffraction, Van der Pauw Hall effect measurements, and low temperature photoluminescence.

Optical nonlinearity in mercury telluride

Mercury telluride is shown to have the largest known third‐order nonlinear optic susceptibility with response time in the picosecond range. At 10.6 μm and T=300 K, χ(3)=1.6×10−4 esu. The response time, estimated from the dispersion of χ(3), is 5 ps. The effect is attributed to interband population modulation. It does not saturate below 1 MW/cm2.

Growth and properties of dilute magnetic semiconductor superlattices containing Hg1−xMnxTe

We report details of the successful growth by molecular beam epitaxy of superlattices containing alternating layers of Hg1−xMnxTe and HgTe. These structures are the first superlattices containing layers of a mercury‐based dilute magnetic semiconductor (Hg1−xMnxTe ) to be grown by any thin‐film technique. The optical and electrical properties of these new magnetic multilayers are discussed.

Free-Carrier Induced Optical Nonlinearities In Semiconductors

HgTe and zero-gap HgCdTe have record, picosecond speed, optical nonlinearities at 10.6μ. They are caused by carrier temperature modulation, which produces large carrier density variations in zero-gap materials. The thermal process is only beginning to saturate at 1 MW/cm2; at that intensity , the dielectric constant of HgTe is modulated by about 10%. Further enhancement of these nonlinearities may be achieved with suitable doping or alloying.

Study of HgTe-cdTe Multilayer Structures by Transmission Electron Microscopy

A transmission electron microscope study of HqTe-CdTe multilayer structures grown by molecular beam epitaxy (MBE) on (100) Cd Zn Te is presented. Both cross-sectional and plain-view observations show highly reaular structures of superlattices and tunnel structures. Dislocation densities estimated by Plan-view observations are of the order of 10 4 cm −2 in these multilayer structures. A quantitative characterization of interface sharpness of superlattices has been carried out by intensity analysis of satellite spots in electron diffraction patterns. It is shown that interfaces in these superlattices are hichly abrupt with a width of one or two monolayers. These observations suggest the effectiveness of the use of lattice-matched substrates to qrow high quality HgTe-CdTe multilayer structures.