Low temperature, postgrowth self-doping of CdTe single crystals due to controlled deviation from stoichiometry

Careful analysis of the Cd-Te pressure-temperature-composition phase diagram, shows a deviation of CdTe stoichiometry only in the Te-depletion direction between 450 and 550 degrees C. Combined control over the semiconductor composition, via intrinsic defects, and over the atmosphere and cooling rate can, therefore, yield a process for intrinsic doping of CdTe at these relatively low temperatures. We present results that support this. Quenching of CdTe, following its annealing in Te atmosphere at 400-550 degrees C, leads to p-type conductivity with a hole concentration of similar to 2 x 10(16) cm(-3). Slow cooling of the samples, after 550 degrees C annealing in Te or in vacuum, increases the hole concentration by one order of magnitude, as compared to quenching at the same temperature. We explain this increase by the defect reaction between Te vacancies and Te interstitials. Annealing in Cd at 400-550 degrees C leads to n-type conductivity with an electron concentration of similar to 2 x 10(16) cm(-3). Annealing at 450-550 degrees C in the equilibrium atmosphere, provided by adding CdTe powder, gives n-type material

N- And P-Type Post-Growth Self-Doping Of Cdte Single Crystals

Careful analysis of the Cd-Te P-T-X phase diagram, allows us to prepare conducting p- and n-type CdTe, by manipulating the native defect equilibria only, without resorting to external dopants. Quenching of CdTe, following its annealing in Te atmosphere at 350-550°C, leads to p-type conductivity with hole concentrations of approx. ~ 2 × 1016 cm-3. Slow cooling of the samples, after 550°C annealing in Te atmosphere, increases the hole concentration by one order of magnitude, as compared to quenching from the same temperature. We explain this increase by the defect reaction between donors VTe and Tei. Annealing in Cd atmosphere in the 350-550°C temperature range leads, in contrast to the annealing in Te atmosphere, to n-type conductivity with electron concentrations of approx. ~ 2 × 1016 cm-3. We ascribe this to annihilation of VCd as a result of Cdi diffusion. © 2000 Elsevier Science B.V

Pyroelectricity in highly stressed quasi-amorphous thin films

Quasi-amorphous BaTiO3 thin films (see Figure) represent a polar ionic solid without spatial periodicity. Most probably, polarity of the quasi-amorphous BaTiO3 is associated with directional ordering of crystal motifs formed in the steep temperature gradient and stabilized by high in-plane mechanical stress. A remarkable characteristic of quasi-amorphous BaTiO3 is expression of strong pyro-and piezoelectric effects in a low dielectric constant material

Formation and thermal stability of quasi-amorphous thin films

The thermal stability of amorphous ionic solids is usually attributed to kinetic considerations related to mass transport. However, there are a number of amorphous ionic solids, which have recently been described, whose unusual resistance to nucleation and subsequent crystallization cannot be explained by mass transport limitations. Examples have been found in a large variety of fields, spanning the range from thin solid films to biomineralization. This poses a question regarding a possible common mechanism for the stabilization of amorphous ionic solids. Here we present a model which explains the formation and thermal stability of quasi-amorphous thin films of BaTiO3, one of the amorphous systems recently described which exhibit unusual thermal stability. On the basis of the experimental evidence presented we suggest that nucleation of the crystalline phase can occur only if the amorphous phase undergoes volume expansion upon heating and transforms into an intermediate low density amorphous phase. If volume expansion is unobstructed by external mechanical constraints, nucleation proceeds freely. However, thin films are clamped by a substrate; therefore, volume expansion is restricted and the low-density intermediate phase is not formed. As a result, under certain conditions, nucleation may be completely suppressed and the phase which appears is quasi-amorphous. A quasi-amorphous film is under compressive stress and as long as the mechanical constraints are in place it remains stable at the temperatures that normally lead to crystallization of amorphous BaTiO3. Quasi-amorphous thin films of BaTiO3 exhibit pyroelectricity, the origin of which is also explained by the proposed model