Epitaxial growth and structure of films of CdTe evaporated in vacuum on to silicon

Abstract

CdTe was evaporated on to (111) surfaces of Xi in an oil-pumped vacuum systcm in pressures in the Torr range. Reproducible epitaxial growth was obtained at all substrate temperatures in the range from 400 to 520 O C . Above this temperature no film could be deposited. The films had the wurtzite structure and the epitaxial orientation relationship was (0001) CdTe parallel to (111) Si with [llZO] CdTe parallel to [I101 Si. The films grown at temperatures in the range from 400 to 500 "C gave transmission electron diffraction patterns that were free of both satellite spots and streaks. This indicated that these films were free both of three-dimensional defects such as twirls and included grains of second phase material and of high densities of planar defects such a s stacking faults. The films grown a t temperatures above 500 "C gave diffraction patterns containing (lOi0) streaks due to faults on the prismatic planes { lOI0).Auf (111)-Oberflgchen von Si wurde in einem Olpumpen-Vakuumsystem bei Driicken im lo-' Tom-Bereich CdTe aufgedampft. Reproduzierbares Epitaxiewachstum wurde bei allen Substrattemperaturen im Bereich von 400 bis 520 "C erhalten. Oberhalb dieser Temperatur konnte keine Schicht aufgebracht werden. Die Schichten hatten Wurtzit-Struktur nnd die Epitaxie-Richtung war (0001) CdTe parallel zu (111) Si mit [llZO] CdTe parallel zu [ l i O ] Si. Schichten, die bei Temperaturen zwischen 400 und 500 "C gewachsen waren, ergaben Transmissions-Elektronenbeugungsdiagramme, die frei von Satellitenpunkten nnd -streifen waren. Dies zeigt, daB diese Schichten sowohl frei sind von drcidimensionalen Storungen, wie Zwillingsgrenzen und EinschluBgrenzen einer zweiten Phase, als auch von ebenen Defekten hoher Dichte, wie Stapelfehlern. Schichten, die oberhalb 500 "C gewachsen waren, ergaben Beugungediagramme mit (lOiO)-Streifen, hervorgerufen durch Stapelfehler auE den { lOI0}-PriamenfIachen,

A soft-solution electrochemical processing technique for preparing CdTe/n-Si(100) heterostructures

“…For example, films grown by UHV sublimation method at a substrate temperature below 250°C exhibited streaked X-ray diffraction patterns which contained extra hexagonal-phase features due to the presence of stacking sequence errors [16]. Similar results have been reported also by Holt and Abdalla [20], who deposited CdTe onto [1 1 1] Si substrates using electron evaporation techniques. Growth routes using gaseous phases require even higher energy than standard high-temperature processes and have resulted in environmental problems because the energy consumed results in exhausted gas(es) or exhaust heat (entropy) [21,22].…”

Some effects of annealing and non-stoichiometry on the structure of epitaxial films of CdTe on Ge

“…In earlier papers the epitaxial growth behaviour and the crystal structures and defect content of films of CdTe evaporated in vacuum on to Ge [l] and on to Si [2] were reported. An obvious means to increase the structural perfection of epitaxial films produced in this way is annealing.…”

Thickness- and Deposition Rate-Dependence of Structural Characteristics of Evaporated CdTe Films

“…and f Te eff = (1-(y+z))f Te + y f V +z f Cd (10) Since the atomic scattering factor of Te is greater than that of Cd, the increase in the absolute values of the measured intensities seems to be a result of the increase of the "effective" scattering factor of f Cd and/or f Te , due to the decrease in the concentration of vacancies (V Cd or V Te ) and/or antisites (Cd Te ). This expected decrease in the density of lattice defects (vacancies and antisites) based on the experimental results of the intensity, is also in agreement with the decrease of the measured microstrain at higher growth rates.…”