## Influence of Applied Bias on Microhardness
The microhardness of CdZnTe exhibits a significant dependence on both the polarity and magnitude of the applied electric bias. This phenomenon is driven by the interaction between the applied electric field and the dislocation dynamics within the crystal. Dislocations are typically the primary carriers of plastic deformation in semiconductors, and their motion can be affected by external electric fields, influencing the material’s mechanical properties.
## Effect of Positive Bias on Microhardness
When a positive bias is applied to CdZnTe, the free carriers (typically holes) in the material are attracted towards the dislocation cores. As a result, holes accumulate at these defect sites, increasing the electrostatic potential around the dislocations. This accumulation of charge at the dislocation cores leads to enhanced pinning, meaning the dislocations are more tightly held in place by the electrostatic interaction with the trapped holes. The increased pinning of dislocations makes it more difficult for them to move, requiring higher stress to overcome the energy barriers associated with dislocation glide. As a result, the material exhibits an increase in microhardness, as the dislocations are less mobile and the resistance to plastic deformation is higher.
## Effect of Negative Bias on Microhardness
In contrast, when a negative bias is applied, electrons are drawn towards the dislocation cores. The presence of excess electrons at the dislocation sites leads to a different electrostatic environment than that seen with positive bias. These trapped electrons can lower the potential energy barriers for dislocation motion, effectively reducing the electrostatic pinning. This reduction in dislocation pinning allows dislocations to move more freely through the crystal lattice under applied stress, resulting in a decrease in microhardness. The material becomes softer because the dislocations can glide more easily, facilitating plastic deformation.
## Magnitude of the Applied Bias
The magnitude of the applied bias further influences the extent to which microhardness is modulated. At low bias voltages, the effect on dislocation pinning is relatively subtle, with only a small change in microhardness. However, as the magnitude of the applied bias increases, the accumulation of charge at the dislocation cores becomes more pronounced, leading to more significant changes in dislocation dynamics and, consequently, microhardness.
* Low Bias: At low bias, the dislocation pinning effect is weak, and the microhardness may only change marginally, either slightly increasing with positive bias or slightly decreasing with negative bias.
* High Bias: At higher bias voltages, the effects become more pronounced, with substantial increases in microhardness under positive bias (due to stronger pinning) and more significant softening under negative bias (due to reduced pinning). The material becomes much harder when dislocations are tightly pinned, and much softer when they are able to move more freely.
## Nonlinear Relationship Between Bias and Hardness
The relationship between bias and microhardness is nonlinear. As the bias increases, the change in microhardness accelerates, particularly under high voltage conditions. The material’s microhardness response may reach a saturation point, where increasing the bias further does not significantly enhance the pinning effect or softening effect. This saturation behavior depends on factors such as the density of dislocations, the intrinsic defect states in the crystal, and the magnitude of the applied electric field.
## Summary
The microhardness of CdZnTe varies significantly with the polarity and magnitude of the applied electric bias. A positive bias enhances microhardness by increasing dislocation pinning through hole accumulation at dislocation cores, making it harder for dislocations to move. Conversely, a negative bias softens the material by attracting electrons to dislocations, reducing pinning and facilitating dislocation motion. The magnitude of the applied bias further modulates these effects, with higher voltages resulting in more pronounced changes in microhardness. The relationship between bias and microhardness is nonlinear, with saturation effects at higher bias voltages.
CdZnTe Association (CdZnTe.com)
https://www.cdznte.com/blog/how-does-the-microhardness-response-of-cdznte-change-with-the-polarity-and-magnitude-of-the-applied-bias.html
