Mahmoud Shaban

Characterization of near-infrared n-type β-FeSi2/p-type Si heterojunction photodiodes at room temperature

n-type β-FeSi2/p-type Si heterojunctions were fabricated from β-FeSi2 films epitaxially grown on Si(111) by facing-target direct-current sputtering. Sharp film-substrate interfaces were confirmed by scanning electron microscopy. The current-voltage and photoresponse characteristics were measured at room temperature. They exhibited good rectifying properties and a change of approximately one order of magnitude in the current at a bias voltage of −1 V under illumination by a 6 mW, 1.31 μm laser. The estimated detectivity was 1.5×109 cm √Hz W at 1.31 μm. The results suggest that the β-FeSi2/Si heterojunctions can be used as near-infrared photodetectors that are compatible with silicon integrated circuits.

n-type β-FeSi2/intrinsic-Si/p-type Si heterojunction photodiodes for near-infrared light detection at room temperature

n-Type β-FeSi2/intrinsic-Si/p-type Si heterojunctions, prepared by facing-targets direct-current sputtering, were evaluated as near-infrared photodetectors. The built-in potential was estimated to be approximately 1 V from capacitance-voltage characteristics. Diodes with a junction area of 0.03 mm2 exhibited a junction capacitance of 4.4 pF at zero bias. At room temperature, the devices exhibited responsivity of 140 mA/W and external quantum efficiency of 13% at a bias voltage of −5 V. The detectivity at zero bias was estimated to be 2.8×109 cm√Hz/W at the wavelength of 1.31 μm. These results indicate their high application potential as near-infrared photodiodes integrated with Si.

Electrical and Photovoltaic Properties of n-Type Nanocrystalline-FeSi2/p-Type Si Heterojunctions Prepared by Facing-Targets Direct-Current Sputtering at Room Temperature

Semiconducting nanocrystalline iron disilicide (NC-FeSi2) thin films were deposited on Si(111) substrates by facing-targets direct-current sputtering at room temperature. The electrical and photovoltaic properties of the n-type NC-FeSi2/p-type Si heterojunctions were measured and investigated. We experimentally proved the possibility of employing this combination in photovoltaics. A large leakage current observed in the current–voltage characteristics, which was predominantly due to the heterojunction interface defects, resulted in a low conversion efficiency.

Near-infrared photodetection of β-FeSi2/Si heterojunction photodiodes at low temperatures

n-type β-FeSi2/p-type Si heterojunction photodiodes were fabricated by facing-targets direct-current sputtering, and their near-infrared photodetection properties were studied in the temperature range of 50–300 K. At 300 K, devices biased at −5 V exhibited a current responsivity of 16.6 mA/W. The measured specific detectivity was remarkably improved from 3.5 × 109 to 1.4 × 1011 cmHz1/2/W as the devices were cooled from 300 K down to 50 K. This improvement is mainly attributable to distinguished suppression in heterojunction leakage current at low temperatures. The obtained results indicate that β-FeSi2/Si heterojunctions offer high potential to be employed as near-infrared photodetectors that are compatible with the current Si technology.

Low-temperature annealing of n-type β-FeSi2/p-type si heterojunctions

β-FeSi2 thin films epitaxially grown on Si(111) were annealed in vacuum at different annealing temperatures. The effects of low-temperature postannealing on the photovoltaic properties of β-FeSi2/Si heterojunctions were investigated. The heterojunctions annealed at 300 °C exhibited an apparent improvement in photovoltaic performance as compared with as-grown heterojunctions. This improvement may be due to Fe atoms, that diffused into the Si substrate during β-FeSi2 film deposition, were gettered by the postannealing process.

Substrate Temperature Dependence of Photovoltaic Properties of β-FeSi2/Si Heterojunctions Prepared by Facing-Target DC Sputtering

We fabricated n-type β-FeSi2/ p-type Si heterojunctions to be used as thin-film solar cells by the facing-target DC sputtering method. The β-FeSi2 films were deposited on Si(111) substrates at different substrate temperatures ranging from 525 to 660 °C. The effect of the substrate temperature on the photovoltaic properties was studied on the basis of the current–voltage characterization and the crystalline structural evaluation of the β-FeSi2/Si heterojunctions. It was found that 600 °C is the optimum substrate temperature suitable for the photovoltaic application.

n-Type Nanocrystalline-

n-Type nanocrystalline-FeSi₂/p-type Si heterojunctions were prepared at room temperature by means of a facing target direct-current sputtering method. The current density-voltage (<i>J</i>- <i>V</i>) characteristics of the devices fabricated were investigated in the temperature range of 77-300 K. At a wavelength of 1.31 μm, the photodiodes exhibited a room-temperature responsivity of 110 mA/cm² and a detectivity of 2.7 × 10⁸ cm√Hz/W, which was improved to 1.5 ×10¹⁰ cm√Hz/W at 77 K. The results profile an attractive low-cost near-infrared photodiode suitable for large-area optoelectronics.

\hbox{FeSi}_{2}

n-Type β-FeSi2/ p-type Si heterojunction solar cells were fabricated. The energy band diagram was derived from the measured ionization potential of β-FeSi2 and well-known parameters. The value of the built-in potential was estimated to be 1.02 V. Under air mass 1.5 illumination, the cell showed a conversion efficiency of 0.63%. The short-circuit current density was 12.81 mA/cm2, whereas the open-circuit voltage was only 176 mV, which might be attributed to the iron atoms that diffused into the Si depletion region. The iron atoms that diffused cause current leakage and also act as trap centers for the photogenerated carriers.

/p-Type Si Heterojunction Photodiodes Prepared at Room Temperature

Heterojunction diodes, which comprise boron-doped p-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films prepared by coaxial arc plasma deposition and n-type Si substrates, were electrically studied. The current–voltage characteristics showed a typical rectification action. An ideality factor of 3.7 in the forward-current implies that carrier transport is accompanied by some processes such as tunneling in addition to the generation–recombination process. From the capacitance–voltage measurements, the built-in potential was estimated to be approximately 0.6 eV, which is in agreement with that in a band diagram prepared on the assumption that carriers are transported in an a-C:H matrix in UNCD/a-C:H. Photodetection for 254 nm monochromatic light, which is predominantly attributable to photocurrents generated in UNCD grains, was evidently confirmed in heterojunctions. Since dangling bonds are detectable by electron spin resonance spectroscopy, their control might be an important key for improving the rectifying action and photodetection performance.

Photovoltaic Properties of n-type β-FeSi2/ p-type Si Heterojunctions

Nitrogen-incorporated ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were synthesized in nitrogen and hydrogen mixed gas atmospheres by coaxial arc plasma deposition. The temperature dependence of electrical resistivity implies that carriers are transported in hopping conduction. Heterojunctions comprising 3 at. % nitrogen-doped films and p-Si substrates exhibited a typical rectifying action. The expansion of a depletion region into the film side was confirmed from the capacitance–voltage characteristics, and the built-in potential and carrier concentration were estimated to be 0.51 eV and 7.5 × 1016 cm−3, respectively. It was experimentally demonstrated that nitrogen-doped UNCD/a-C:H is applicable as an n-type semiconductor.