InSb/CdTe Heterostructures Grown by Molecular Beam Epitaxy

Given the potential for quantum effect device application, the growth, by molecular beam epitaxy, and characterization of InSb-CdTe heterostructures is described. Two procedures for growth of these heterostructures are employed. For the growth of InSb/CdTe double heterostructures, InSb and CdTe layers are grown in separate MBE growth chambers connected via an ultrahigh vacuum transfer module. Here, antimony originating from a compound InSb source oven is used for growth of InSb layers. For the growth of CdTe/InSb multiple quantum well structures, InSb and CdTe layers are grown in a single MBE growth chamber, where antimony is derived from an antimony cracking furnace. To study the optical nature of heteroepitaxially grown InSb, infrared photoluminescence from InSb based double heterostructures has been examined. Despite the transferral of grown layers between III-V and II-VI chambers, luminescence gathered from thick” InSb active layers has shown the existence of recombination features which are similar to bulk InSb. For multilayer structures, grown in a single chamber with the use of an antimony cracker, emphasis has been placed on structural examination by transmission electron microscopy and x-ray diffraction techniques. Examination of multilayer structures by transmission electron microscopy suggests tha t the cracker may be useful for the growth of InSb at low substrate temperatures and low growth rates. Using the cracker, CdTe/InSb superlattice structures have been grown showing multiple satellite peaks in the x-ray diffraction spectrum

Molecular Beam Epitaxy of ZnSe on GaAs Epilayers for Use in MIS Devices

The use of ZnSe on GaAs epilayers (epi) as a pseudo-insulator in field effect device applications is demonstrated. The passivating ZnSe layers are grown on GaAs(epi) by interrupted growth molecular beam epitaxy (MBE) using two separate MBE machines. A thin layer of amorphous arsenic protects the GaAs(epi) during transfer between the MBE systems. When nucleated on the GaAs(epi), the ZnSe grows layer-by-layer as revealed by the reflection high energy electron diffraction pattern generated in the II-VI MBE growth chamber. A study of intensity oscillations in the electron diffraction pattern is further used to understand the initial growth stages of ZnSe on GaAs(epi). The material properties of the ZnSe/GaAs(epi) heterostructure are briefly examined. Even though ZnSe and GaAs have a 0.25% lattice mismatch, transmission electron micrographs show that very thin films (1OOOA) of ZnSe form a coherent and dislocation free interface with the GaAs(epi). In thicker ZnSe films, strain relieving misfit dislocations are observed. Photoluminescence measurements reveal information about the effect of the lattice mismatch on the energy band structure of the ZnSe. For the 1OOOA film, the excitonic features are shifted upwards in energy, and the normally degenerate light and heavy hole valence bands split into two bands. As the 1OOOA of ZnSe is an appropriate thickness for an insulator in a field-effect device, the ZnSe/ GaAs(epi) heterostructure is then used in metal-insulator-semiconductor (MIS) capacitors and transistors. Most prominent, the fabrication of the first depletion-mode field-effect transistors based on the ZnSe/n-GaAs heterointerface are described. The transistors display near ideal characteristics with complete current saturation and cutoff; the channel modulation indicates th a t the Fermi level is not pinned a t the ZnSe/n-GaAs interface. With the success of the depletion-mode transistors, the use of ZnSe and GaAs(epi) in future MIS devices appears promisin

Zinc Oxide-on-Silicon Surface Acoustic Wave Devices

A monolithic ZnO-on-silicon surface acoustic wave (SAW) memory correlator has been fabricated which utilizes induced junctions separated by ion implanted regions to store a reference signal. The performance characteristics of this device have been investigated including storage time, dynamic range, and degenerate convolution efficiency. Verification of the existence of charge storage regions is possible prior to completed device fabrication. A theory explaining the charge storage process is developed and applied to the implant-isolated storage correlator. The implant-isolated correlator theory is applied to related structures which employ slightly different storage mechanisms. The ion implanted correlator is used to determine the wave potential associated with a propagating SAW. Characteristics of ZnO-on-Si SAW resonators with sputtered ZnO films limited to the interdigital transducer (IDT) regions are investigated. Upper limits on propagation loss for surface waves on silicon substrates are determined by employing externally coupled limited ZnO SAW resonators. Resonator Q-values are enhanced by restricting the lossy ZnO area and predictions are made as to achievable Q-values for resonators fabricated in the externally coupled configuration. Experimental results for limited ZnO, internally coupled ZnO-on-Si resonators are also given. A complete theory for the mode conversion resonator is presented which predicts the array separation for proper device operation. The theory also gives way to a special condition for spatial ndependence of resonator output with respect to IDT placement. Mode conversion resonators are fabricated which experimentally verify these predictions

Temperature dependence of strain in ZnSe(epilayer)/GaAs(epilayer)

doi:10.1063/1.360477A study of biaxial strain as a function of temperature in a ZnSe epilayer grown on a GaAs substrate is presented. The strains are determined by measuring the heavy‐ and light‐hole related excitonic transitions via photomodulated spectroscopy. The strain is found to increase with increasing temperature. The data are compared with a calculation using a previously determined elastic constant and thermal expansion coefficients. The temperature dependence determined here allows a comparison of various other optical measurements performed at different temperatures.The work by H. R. C. was supported in part by the U. S. Department of Energy under Contract No. DE-FG02-89ER45402. M. C. acknowledges the support from the U.S. Army Research Office DAAL-03-92-G0381. A. K.. R. acknowledges support from the National Science Foundation (Materials Research Group No. DMR89-13706) and R. L. G. from AFOSR-89-0438; both A. K. R. and R. L. G. also acknowledge support from DARPA-URI Grant No. 218-25015. We thank Lok C. Lew Yan Voon and L. R. Ram-Mohan for many stimulating discussions

Pressure tuning of strain in CdTe/InSb epilayer: A photoluminescence and photomodulated reflectivity study

doi:10.1063/1.354415The heavy‐hole and light‐hole excitons of a CdTe epilayer, pseudomorphically grown on an InSb epilayer by molecular beam epitaxy, are studied with a diamond anvil cell as a function of applied hydrostatic pressure via photoluminescence (PL) and photomodulated reflectivity (PR) spectroscopies. They are compared with the excitonic features in the simultaneously measured PL spectra of a sample of bulk CdTe. Under applied pressure, the lattice mismatch‐induced splitting between the light‐hole and heavy‐hole related transitions increases in a continuous and reversible manner because of the additional pressure‐induced compression due to the difference in the compressibilities of CdTe and InSb. The unusually large strain sustained by the CdTe epilayer under pressure is discussed in the light of various models. The PR signal vanishes after the InSb epilayer goes through a structural phase transition at approximately 20 kbar, while the PL signal persists until it is irreversibly quenched by the CdTe epilayer undergoing a structural phase transition at approximately 30 kbar. For pressures between 20 and 30 kbar, the behavior of the CdTe epilayer is similar to that of the bulk sample; the strain appears to have been relaxed due to the structural phase transition which has taken place in InSb. Values of the first‐ and second‐order pressure coefficients for bulk CdTe and for the CdTe epilayer as well as values of the hydrostatic and shear deformation potentials are obtained at 14 and 80 K and compared with previously quoted values.The work by H.R.C. was supported in part by the U.S. Department of Energy under Contract No. DE-FG02-89ER45402. M.C. acknowledges partial support from the Research Corporation and the U.S. Army Grant No. DAAL-03-92-G-038 1. M.S.B. acknowledges partial support by the G. Ellsworth Huggins Fellowship. A.K.R. and R.L.G. acknowledge support from the National Science Foundation (Materials Research Group No. DMR89-13706)

Research on nonlinear optical materials: an assessment

The seven papers making up this assessment are based on the Workshop on Nonlinear Optical Materials held in April 1986