Region Recombination (Device menu)
This selection allows you to specify the recombination parameters in the bulk and at both the front and rear surface of the region.
The bulk recombination model used by PC1D supplies a single Shockley-Read-Hall (SRH) energy level with separate electron and hole lifetimes and an adjustable trap energy level within the bandgap. The dialog box for specifying these parameters for the current region can also be opened using a button on the toolbar. This toolbar button will appear to be depressed if the electron or hole lifetime has been altered from its default value of 1 ms.
The trap level, Et, is specified with respect to the intrinsic level, which lies near the middle of the bandgap. The electron and hole lifetimes specified at the top of the dialog box are the values corresponding to intrinsic material at a temperature of 300 K.
Also listed in the bulk-recombination dialog box is the excess-carrier lifetime in low-level injection and the corresponding diffusion length, for material with the background doping and reference temperature specified in the dialog box. These calculated values include the effect of band-to-band and Auger recombination, the coefficients for which are specified for the material's band structure in this region, and also the effects of background doping on the SRH lifetimes as specified in the material recombination dialog.. To obtain a specific low-level-injection lifetime or diffusion length, simply type the desired number in the space provided. PC1D will calculate the intrinsic electron and hole lifetimes needed. Note that the properties of the material (band-to-band, Auger recombination, etc.) place an upper limit on the achievable lifetime and diffusion length for a given background doping density.
Front/Rear Surface Recombination
The surface recombination model used by PC1D supplies a single Shockley-Read-Hall (SRH) energy level with separate electron and hole lifetimes and an adjustable trap energy level within the bandgap. . The dialog box for specifying these parameters for the front or rear surface of the current region can also be opened using buttons on the toolbar. These toolbar buttons will appear to be depressed if there is recombination at that surface. When either Sn or Sp is nonzero, the SRH surface recombination rate is given by
The trap level, Et, is specified with respect to the intrinsic level, which lies near the middle of the bandgap. The electron and hole surface recombination velocities specified at the top of the dialog box are the values corresponding to intrinsic material at the reference temperature specified in the dialog box. The values of Sn and Sp entered are modified for use in the recombination formula to reflect the actual device temperature and the surface doping density. The extent of this modification depends on the parameters listed in the material recombination dialog box.
Also listed in the surface-recombination dialog box is the effective minority-carrier surface recombination velocity for material with the surface doping at a temperature of 300 K. To obtain a specific minority-carrier surface recombination velocity, simply type the desired number in the space provided. PC1D will calculate the intrinsic electron and hole surface recombination velocities needed.
When high-level injection occurs at the surface, you can choose to either continue with the Shockley-Read-Hall model (the “S” model), or you can choose instead to maintain the saturation current density at the surface at the same value it had in low-level injection:
The choice of high-level-injection model for surface recombination has no effect when the surface remains in low-level injection.
Important Note on Surface Recombination
When there is more than one region in the device, the front and back surfaces refer to the current region, not the device as a whole. The recombination rate calculated for the back surface of region 1 is added to the recombination rate calculated for the front surface of region 2 to get the total rate of recombination at the interface between the two regions.