Thermomigration of Te precipitates and improvement of (Cd,Zn)Te substrate characteristics for the fabrication of LWIR (Hg, Cd)Te photodiodes

Bulk Growth of CdZnTe/CdTe Crystals

“…They concluded [5] that part of the vacancies would become occupied by impurity atoms, thereby mainly producing acceptor-type centers. These centers (possibly together with unoccupied vacancies that also have acceptor character) are the source of the p-type conductivity [6]. Despite some differences in the technical details, the predominant acceptor defect has been assumed to be the cadmium vacancy V Cd and this is responsible for the p-type conductivity [7].…”

“…In order to reduce the Te precipitates, Vydyanath et al [6,11] carried out wafer annealing of CdZnTe containing Te precipitates, over the temperature range of 500-900 • C, using Cd/Zn pressures appropriate to stoichiometry, and postulated that the reported removal of large Te precipitates could result from migration of the second-phase material under the action of temperature gradients if the Te melting point is exceeded during the wafer annealing. However, it is noted that this process may be at the expense of an increase in dislocation density and rocking curve width.…”

“…However, in the case of incomplete annealing, the crystal showed n-type conductivity with a large size (10 µm) of Cd precipitates. Vydyanath et al [6,11] have shown that the existence of a temperature gradient in the CdTe wafers is necessary for the process of Te precipitate thermomigration to occur during the annealing. However, the present postgrowth ingot annealing was performed at the same temperature from top to tail of the ingots.…”

“…The effect of wafer annealing on the precipitates in CdZnTe crystals has been widely studied. Vydyanath et al [6] showed that the IR transmittance is increased by eliminating the Te precipitates after annealing at 800-900 • C under Cd and Zn overpressure. It has been shown that the annealing can modify the electrical properties, increase the IR transmittance and reduce the precipitate density.…”

Infrared transmission spectra of Cd1−xZnxTe (x = 0.04) crystals

“…Processes of step wafer annealing under well-controlled thermodynamic conditions are widely used to eliminate most Te-rich phases present in CZT substrates. 1,2 The vertical gradient freezing method with a Cd reservoir has been developed to grow CZT crystals with less or even no Te-rich phases. 3,4 The Te-rich phases are thought to be the main source of deterioration of the IR transmittance.…”