CdTe is one of the leading materials used in solar photovoltaics. However, the maximum reported CdTe cell efficiencies are considerably lower than the theoretically expected efficiencies for the ∼1.48 eV CdTe band gap. We report a class of single crystal CdTe-based solar cells grown epitaxially on crystalline Si that show promise for enhancing the efficiency and greatly lowering the cost per watt of single-junction and multijunction solar cells. The current-voltage results for our CdZnTe on Si solar cells show open-circuit voltages significantly higher than previously reported for any II-VI cells and as close to the thermodynamic limit as the best III-V-based cells.

Articles you may be interested inQuantum efficiency investigations of type-II InAs/GaSb midwave infrared superlattice photodetectors J. Appl. Phys. 116, 043101 (2014); 10.1063/1.4890309High operating temperature midwave infrared photodiodes and focal plane arrays based on type-II InAs/GaSb superlattices Appl.Eye-safe midwavelength infrared InAs-GaSb strain layer superlattice p + -n − -n homojunction avalanche photodiodes ͑APDs͒ grown by solid source molecular beam epitaxy were fabricated and characterized. Maximum multiplication gain of 1800 was measured at −20 V at 77 K. Excess noise factors between 0.8 and 1.2 were measured up to gain of 300. Gain of 200 was measured at 120 K. Exponential nature of the gain as a function of reverse bias along with low excess noise factor at higher gain confirms single carrier electron-only impact ionization in the avalanche regime. Decrease in the multiplication gain at higher temperatures correlates with standard APD characteristics.

Silicon dioxide (SiO 2 ), silicon nitride (Si x N y ), and zinc sulfide (ZnS) with ammonium sulfide [(NH 4 ) 2 S] as a prepassivation surface treatment were compared as passivants for InAs/GaSb strained layer superlattice detectors with a 0% cutoff wavelength of $10 lm. SiO 2 did not show significant improvement and the zero-bias resistance-area product (R 0 A) was 0.72 X-cm 2 at 77 K. Si x N y passivation showed a nominal improvement with an R 0 A value of 4.1 X-cm 2 at 77 K. ZnS with (NH 4 ) 2 S treatment outperformed others significantly, improving the R 0 A value to 492 X-cm 2 at 77 K. Variable-area diode measurements indicated a bulk-limited R 0 A value of 722 X-cm 2 . ZnS-passivated diodes exhibited maximum surface resistivity with a value of 2500 X-cm.

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Mid-wavelength infrared (MWIR) p + -n --n + avalanche photodiodes (APDs) were fabricated using two materials systems, one with mercury cadmium telluride (HgCdTe) on a silicon (Si) substrate and the other with an indium arsenide/gallium antimonide (InAs/GaSb) strained layer superlattice (SLS). Diode characteristics, avalanche characteristics, and excess noise factors were measured for both sets of devices. Maximum zero-bias resistance times active area (R 0 A) of 3 9 10 6 X cm 2 and 1.1 9 10 6 X cm 2 and maximum multiplication gains of 1250 at -10 V and 1800 at -20 V were measured for the HgCdTe and the SLS, respectively, at 77 K. Gains reduce to 200 in either case at 120 K. Excess noise factors were almost constant with increasing gain and were measured in the range of 1 to 1.2.