It is known that boron is one of the most commonly used impurities in silicon technology, e.g. Schematic representation of the pn structures after processing: (a) on n-Si wafers with different resistivity (Si70) and (Si10); (b) on SOI, a, b. On the contrary, a lower intensity of the signal indicates severe damage to the crystal structure.
In the ion-implanted material, an increase in interplanar spacing and of the lattice constant is observed [17]. Dose dependence of the Raman spectra parameters: (a) change in the main band position (position of the reference sample maximum is 520 сm−1); (b) intensity (red), half-width (black). After implantation and annealing, an increase in the band intensity of the Si-O oscillations (1082 cm−1) is observed [19, 21].
The effect of annealing temperature on the photoresponse spectra of Si70 samples implanted with a dose of 1 × 1014 cm−2 and annealed at different temperatures was studied in [19]. It was shown that the position of the main peak in the SWIR region, similar to the dose dependence, does not depend on the annealing temperature. Spectral dependence of the integral relative photosensitivity for the p-n-Si(B) structure at a dose of 6 × 1014 сm−2.
The behavior of the UV photoresponse for the other two doses used is almost the same.
Discussion
As can be seen from the figure, the annealing temperature has a completely different effect on the photosensitivity in the UV and IR spectral range. It is interesting to note that in the 1000°C annealing temperature regime, the photoresponse signals in the IR region are practically identical for all three implantation doses. Regardless of the doses for Si70 and Si10, some defects form DL in the band gap with activation energies of about 0.7 and 0.65 eV.
The corresponding maxima (main and smooth) in the photosensitivity spectra are characterized by their intensities that vary with respect to their dose and annealing dependence. The increase in the intensity of photosensitivity up to the dose of 6 × 1014 cm−2 is associated with the increasing concentration of these defects. A sharp increase in intensity and a noticeable decrease in the half-width of the band at 77 K indicate an increase in the occupancy of DL formed by defects responsible for photosensitivity (Figure 8).
The behavior of leakage currents (Figure 5) at high doses II and annealing at 900°C can be described by the formation of new dislocation-type defects, part of which leads to generation-recombination processes in the space charge region and affects the reverse current in the diode. The understanding of the defect formation mechanism becomes even more complicated due to the observed correlation between the content of carbon and oxygen impurities in the surface layer and the IR photoresponse at different doses and annealing regimes (Figure 15). The role of carbon may be rather indirect, as an increase in the carbon content reduces the concentration of oxygen obtained.
The coefficient of light absorption in this spectral range is α сm−1 and the corresponding depth of absorption is of the order of 1 μm. The appearance of areas with a negative photoresponse depends on the spectral composition of the incident light, and the intensity at the same annealing temperature (900, 20 min) depends on the dose II, which increases from 1 × 1014 to 6 × 1014 сm−2. The population of these levels depends on the spectral composition of the light, and their concentration and depth are determined by the conditions of the ion doping treatment.
At high EMR energies in the UV range, absorption processes must take place in the surface layer. Most likely, the intensity of the UV photoresponse should increase with the annealing temperature due to the decrease in the concentration of trap centers. Therefore, by using a damaged layer in the output material, the controlled photoelectric properties of p-n structures can be realized, and this process is proposed as an innovative approach to the development of SWIR array photodetectors.
Conclusions
Another interesting effect is observed on the integrated photosensitivity spectra (Figure 14) at EMR energies exceeding the bandgap value of silicon - the appearance of regions of zero and negative photosensitivity. The observed negative photosensitivity is apparently due to the presence of surface levels in p-n-Si(B) structures, which are capture centers of most charge carriers. It is clear from the data of Figure 16 that the mechanisms of photoresponse in SWIR and UV regions are completely different.
In general, the interpretation of some of the data obtained and the underlying physical mechanisms needs additional clarification. It is important to note that the technique itself and the measurement results are highly reproducible. In this regard, high-resistance n-Si samples implanted with a dose of B+ 6 × 1014 сm−2 and annealed at 900 °C (20 min) can find practical application as SWIR pixel arrays.
Based on SOI structures, a quasi-planar array can be developed, especially for those cases where a relatively weak output signal is "compensated". A well-defined correlation between the structural, electrical and photoelectric properties in SWIR and UV regions on the one hand, and implantation and annealing regimes, as well as C and O impurity content on the other hand, is demonstrated. In the starting material, a damaged layer on the surface with a thickness of hundreds of nanometers was found to have a significant effect on the results obtained.
The effects observed in the SWIR range are discussed in terms of the formation/transformation of extended defects with DL (0.7 and 0.65 eV for Si70 and Si10, 0.72 and 0.61 eV for SOI) in the material , most likely dislocation loops. The photoresponse intensity in the UV range appears to be related to a change in the concentration of trap centers in the near surface layer of pn-Si(B) structures. The areas of negative photoresponse observed on the integrated photosensitivity spectra depend on the spectral composition of the incident light.
We attribute this effect to the presence of major charge carrier trapping centers in the near-surface layers of the sample. Taking into account that the technology itself and the results of the measurements are well reproducible for different single-crystal n-Si, it is obvious that the implantation of boron enables a controlled change of the photoelectric properties of the material. The obtained results can be used for the development of SWIR pixels and quasi-planar arrays and UV detectors.
Acknowledgements
Author details
Diode characteristics and residual deep defects of p+-n junctions fabricated with rapid heat implanted silicon. Analysis of the influence of technological parameters and the type of photodetectors on their photosensitivity in the UV spectral range. In: Proceedings of the 6th All-Slovenian Youth School "Materials of nano-micro- and optoelectronic technology: physical".
In: Proceedings of the 2nd International Conference on Modern Technologies and Methods of Anorganic Materials Science; 20-24 april 2015; Tbilisi, Georgië. In: Proceedings of the International Conference on Gettering Defect Engineering in Semiconductor Technology XVI; 20-25 september 2015; Bad Staffelstein, Duitsland. In: Proceedings of the International Conference on Gettering Defect Engineering in Semiconductor Technology XVII; 1-6 oktober 2017; Lopota Resort, Georgië.
Effect of ion doping on silicon photoluminescence originating from dislocations formed by implantation of Si+ ions. Effect of pre-annealing of silicon substrates on the spectral sensitivity of photodetectors in bipolar integrated circuits. A selection of our books indexed in the Book Citation Index in the Web of Science™ Core Collection (BKCI).
TOP 1%
- Introduction
- SIMS profile
- Other dopants
- TEM characterization
- Arsenic
- Other dopants
- XRD analysis
- Computer simulation
- Conclusion
Furthermore, the microstructures of the induced damages in MCT implanted with group V dopants (N, P, As and Sb) were investigated [16]. It can be seen from Figure 1 that the end-of-range (EOR) depth of As-implanted arsenic ions increases with the implant energy. The SIMS profiles of the arsenic ions implanted in MCT epilayer without barrier layer at 320 keV with different doses are illustrated in Figure 2(a) .
The arsenic profiles of the MCT sample with CdTe barrier layer before and after annealing are illustrated in Figure 6. On the other hand, the lower EOR depth of the ZnS coated sample implanted with arsenic ions at higher energy shows that the ZnS layer has stronger barrier ability than CdTe. In addition, the profiles of the other group V dopants implanted in the MCT were characterized by SIMS.
In contrast, the movement of arsenic ions implanted in MCTs depends mainly on lattice atom displacements and replacements due to ion–atom collisions. Then, the microstructures of surface amorphization and induced defects in MCT epilayers implanted with arsenic and phosphorus ions will be characterized and analyzed by TEM. It appears that a longer ion implantation, equivalent to a higher dose, could induce amorphization of the surface MCT.
In addition, the insensitivity of the thickness of the entire damage layer to beam current implies that the SDL could be transformed to the α-MCT layer under the successive ion bombardment. The high-resolution TEM was used to characterize the detailed microstructures of the induced defects in the SDL of arsenic-implanted MCT layers. Here, the TEM cross-sectional images of the bilayer ZnS-coated MCT epilayer (implanted with arsenic at 400 keV) and the bilayer CdTe-coated MCT epilayer (implanted with arsenic at 320 keV) are shown in Figure 12, respectively.
The a-MCT layers become very thin or almost disappear both in the MCT epilayers of the two samples. The a-MCT and SDL layer thicknesses in the phosphor implanted sample are about 380 and 220 nm, respectively. By undergoing ion implantation, the FWHMs of the characteristic peaks of the implanted MCT epilayers are all broadened.
Therefore, the FWHM and the position of the broad peak are related to the amorphization of the surface MCT layer. Histogram of the simulation and experimental Rp values of arsenic ions implanted in the ZnS-coated and CdTe-coated MCT epilayers.
