| 1. |
- Adnane, Bouchaib, et al.
(författare)
-
Origin of photoresponse at 8-14 μm in stacks of self-assembled SiGe/Si quantum dots
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A normal incidence photodetector operating at 8-14 μm is demonstrated using p-type δ-doped SiGe dot multilayer structures grown by molecular beam epitaxy on Si(001) substrates. Based on the experimental results of photoluminescence and photoluminescence excitation spectroscopies together with numerical analysis, the origin of the measured photocurrent was attributed to intersubband optical transitions between the heavy hole and light hole states of the valence band of the self-assembled SiGe dots and subsequent lateral transport of photo-excited carriers in the conduction channels formed by Ge wetting layers.
|
|
| 2. |
- Adnane, Bouchaib, et al.
(författare)
-
Photoluminescence excitation spectroscopy of self-assembled SiGe/Si quantum dots
- 2009
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Photoluminescence excitation (PLE) experiments are reported for various self-assembled SiGe/Si dot samples grown on Si(001) by molecular beam epitaxy at substrate temperatures ranging from 430 to 580 C. Two excitation peaks were observed, and the characteristics of the involved optical transitions were studied in detail by PLE (in one case implemented together with selective photoluminescence, SPL) on different samples containing either only one SiGe dot layer or multiple SiGe-dot/Si stacks. The temperature- and power-dependence of the excitation properties together with the results of six-band k.p calculations support the assignment of the observed PLE peaks to spatially direct and indirect transitions collected from two different SiGe dot populations.
|
|
| 3. |
- Adnane, Bouchaib, et al.
(författare)
-
Photoluminescence study of nanocrystalline-Si(Ge) embedded in mesoporous silica
- 2009
-
Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 53:8, s. 862-864
-
Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) properties of mesoporous silica (MS) samples incorporated with Si or Ge nanocrystals (nc) have been investigated with various excitation powers and post-RTA processes. The analysis of experimental results revealed a superlinear intensity dependence (m = 1.7) in the MS reference sample without nanocrystals, while a sublinear behavior (m = 0.8) is observed for the nc-Si in MS. It thus suggests the same recombination responsible for the luminescence at similar to 2.75 eV for both samples, but different kinetic limitations for the carrier transfer processes. Si nanocrystals play in this case an important role in generating more photo-excited carriers, enhancing the PL intensity.
|
|
| 4. |
- Chen, P.Y., et al.
(författare)
-
Synthesis design of artificial magnetic metamaterials using a genetic algorithm
- 2008
-
Ingår i: Optics Express. - 1094-4087. ; 16:17, s. 12806-12818
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, we present a genetic algorithm (GA) as one branch of artificial intelligence (AI) for the optimization-design of the artificial magnetic metamaterial whose structure is automatically generated by computer through the filling element methodology. A representative design example, metamaterials with permeability of negative unity, is investigated and the optimized structures found by the GA are presented. It is also demonstrated that our approach is effective for the synthesis of functional magnetic and electric metamaterials with optimal structures. This GA-based optimization-design technique shows great versatility and applicability in the design of functional metamaterials. © 2008 Optical Society of America.
|
|
| 5. |
- Cheng, M.H., et al.
(författare)
-
Growth and characterization of Ge nanostructures selectively grown on patterned Si
- 2008
-
Ingår i: Thin Solid Films. - : Elsevier Science B.V., Amsterdam.. - 0040-6090 .- 1879-2731. ; 517:1, s. 57-61
-
Tidskriftsartikel (refereegranskat)abstract
- By utilizing different distribution of strain fields around the edges of oxide, which are dominated by a series of sizes of oxide-patterned windows, long-range ordered self-assembly Ge nanostructures, such as nano-rings, nano-disks and nano-dots, were selectively grown by ultra high vacuum chemical vapor deposition (UHV-CVD) on Si (001) substrates. High-resolution double-crystal symmetrical omega/2 theta scans and two-dimensional reciprocal space mapping (2D-RSM) technologies employing the triple axis X-ray diffractometry have been used to evaluate the quality and strain status of as-deposited as well as in-situ annealed Ge nanostructures. Furthermore, we also compare the quality and strain status of Ge epilayers grown on planar unpatterned Si substrates. It was found that the quality of all Ge epitaxial structures is improved after in-situ annealing process and the quality of Ge nano-disk structures is better than that of Ge epilayers; on planar unpatterned Si substrates, because oxide sidewalls are effective dislocation sinks. We also noted that the degree of relaxation for as-deposited Ge epilayers on planar unpatterned Si substrates is less than that for as-deposited Ge nano-disk structures. After in-situ annealing process,all Ge epitaxial structures are almost at full relaxation whatever Ge epitaxial structures grew on patterned or unpatterned Si substrates.
|
|
| 6. |
- Elfving, Anders, et al.
(författare)
-
Asymmetric relaxation of SiGe/Si(110) investigated by high-resolution x-ray diffraction reciprocal space mapping
- 2006
-
Ingår i: Applied physics letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89, s. 181901-1--181901-3
-
Tidskriftsartikel (refereegranskat)abstract
- Strain relaxation of SiGe/Si(110) has been studied by x-ray reciprocal space mapping. To get information about the in-plane lattice mismatch in different directions, two-dimensional maps around, e.g., (260) and (062) reciprocal lattice points have been obtained from Si0.8Ge0.2/Si(110) samples, which were exposed to different annealing conditions. The in-plane lattice mismatch was found to be asymmetric with the major strain relaxation observed in the lateral [001] direction. This was associated with the formation and propagation of dislocations oriented along [10]. The relaxation of as-grown structures during postannealing is thus different from relaxation during growth, which is mainly along [10].
|
|
| 7. |
- Elfving, Anders, 1976-
(författare)
-
Near-infrared photodetectors based on Si/SiGe nanostructures
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two types of photodetectors containing Ge/Si quantum dots have been fabricated based on materials grown by molecular beam epitaxy and characterized with several experimental techniques. The aim was to study new device architectures with the implementation of Ge nanostructures, in order to obtain high detection efficiency in the near infrared range at room temperature.Heterojunction bipolar phototransistors were fabricated with 10 Ge dot layers in the base-collector (b-c) junction. With the illumination of near infrared radiation at 1.31 to 1.55 µm, the incident light would excite the carriers. The applied field across the b-c junction caused hole transport into the base, leading to a reduced potential barrier between the emitter-base (e-b) junction. Subsequently, this resulted in enhanced injection of electrons across the base into the collector, i.e., forming an amplified photo-induced current. We have therefore obtained significantly enhanced photo-response for the Ge-dot based phototransistors, compared to corresponding quantum dot p-i-n photodiodes. Responsivity values up to 470 mA/W were measured at 1.31 µm using waveguide geometry, and ∼2.5 A/W at 850 nm, while the dark current was as low as 0.01 mA/cm2 at –2 V.Metal-oxide field-effect phototransistors were also studied. These lateral detectors were processed with three terminals for source, drain and gate contacts. The Ge quantum dot layers were sandwiched between pseudomorphically grown SiGe quantum wells. The detector devices were processed using a multi-finger comb structure with an isolated gate contact on top of each finger and patterned metal contacts on the side edges for source and drain. It was found that the photo-responsivity was increased by a factor of more than 20 when a proper gate bias was applied. With VG above threshold, the measured response was 350 and >30 mA/W at 1.31 and 1.55 µm, respectively.Properties of Si/Si1-xGex nanostructures were examined, in order to facilitate proper design of the above mentioned transistor types of photodetectors. The carrier recombination processes were characterized by photoluminescence measurements, and the results revealed a gradual change from spatially indirect to direct transitions in type II Si1-xGex islands with increased measurement temperature. Energy dispersive X-ray spectrometry of buried Ge islands produced at different temperatures indicated a gradual decrease of the Ge concentration with temperature, which was due to the enhanced intermixing of Si and Ge atoms. At a deposition temperature of 730°C the Ge concentration was as low as around 40 %.Finally, the thermal stability of the Si/SiGe(110) material system, which is a promising candidate for future CMOS technology due to its high carrier mobility, was investigated by high resolution X-ray diffraction reciprocal space mapping. Anisotropic strain relaxation was observed with maximum in-plane lattice mismatch in the [001] direction.
|
|
| 8. |
- Elfving, Anders, et al.
(författare)
-
Three-terminal Ge dot/SiGe quantum-well photodetectors for near-infrared light detection
- 2006
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89, s. 083510-083513
-
Tidskriftsartikel (refereegranskat)abstract
- A three-terminal metal-oxide-semiconductor field-effect transistor type of photodetector has been fabricated with a multiple stack of Ge dot/SiGe quantum-well heterostructures as the active region for light detection at 1.3–1.55 µm. Gate-dependent edge incidence photoconductivity measurements at room temperature revealed a strong dependence of the photoresponse on the gate voltage. At positive gate bias, the hole transport from the dots into the wells was improved, resulting in a faster response. The high photoresponsivity at negative VG, measured to be 350 mA W–1 at 1.31 µm and 30 mA W–1 at 1.55 µm, was ascribed to the photoconductive gain.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
- Gomes, P.F., et al.
(författare)
-
Type-I optical emissions in GeSi quantum dots
- 2007
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 91:5
-
Tidskriftsartikel (refereegranskat)abstract
- The authors studied the optical emission of GeSi quantum dots under externally applied biaxial stress using samples grown with different temperatures varying from 430 to 700 °C. The optical emission energy of samples grown at low temperatures is rather insensitive to the applied external stress, consistent with the type-II band alignment. However, for samples grown at high temperatures we observed a large blueshift, which suggests type-I alignment. The result implies that recombination strength can be controlled by the growth temperature, which can be useful for optical device applications. © 2007 American Institute of Physics.
|
|
| 12. |
- Karim, Amir, 1976-, et al.
(författare)
-
Characterization of Er/O-doped Si-LEDs with low thermal quenching
- 2005
-
Ingår i: Material Research Society Symposium Proceedings. ; , s. 117-124
-
Konferensbidrag (refereegranskat)abstract
- Electroluminescence studies of MBE-grown Er/O-doped Si-diodes at reverse bias have been done. For some devices there is much reduced thermal quenching of the emission at 1.54 µm. There are examples where the temperature dependence is abnormal in that the intensity for a constant current even increases with temperature up to e.g. 80 oC. These devices have been studied with cross-sectional transmission electron microscopy to see the microstructure of the Er/O-doped layers as well as the B-doped SiGe-layers that are used as electron emitters during reverse bias. Although there are defects in the layers there is no evidence for large thick precipitates of SiO2. While reduced thermal quenching often is attributed to having the Er-ions within SiO2 layers, this is not the case for our structures as evidenced by our TEM-studies. The origin of the abnormal temperature dependence is attributed to the two mechanisms of breakdown in the reverse-biased diodes. At low temperature the breakdown current is mainly due to avalanche resulting in low-energy electrons and holes that quenches the intensity by Auger de-excitation of the Er-ions. At higher temperature the breakdown current is mainly phonon-assisted tunnelling which results in a more efficient pumping with less de-excitation of the Er-ions. Finally at the highest temperatures the thermal quenching sets in corresponding to an activation energy of 125 meV, which is slightly lower than 150 meV that has been reported in other studies.
|
|
| 13. |
- Karim, Amir, 1976-, et al.
(författare)
-
Compositional analysis of Si/SiGe quantum dots using STEM and EDX
- 2006
-
Ingår i: Volume 6129 - Quantum Dots, Particles, and Nanoclusters III, Proceedings of SPIE. - : SPIE.
-
Konferensbidrag (refereegranskat)abstract
- Ge islands fabricated on Si(100) by molecular beam epitaxy at different growth temperatures, were studied using crosssectional scanning transmission electron microscopy and energy-dispersive X-ray spectrometry combined with electron energy loss spectrometry experiments. The island size, shape, strain, and material composition define the dot-related optical transition energies, but they are all strongly dependent on the growth temperature. We have performed quantitative investigations of the material composition of Ge/Si(001) quantum dots. The samples were grown at temperatures ranging from 430 to 730 °C, with one buried and one uncapped layer of Ge islands separated by 140 nm intrinsic Si. The measurements showed a Ge concentration very close to 100 % in the islands of samples grown at 430 °C. With a growth temperature of 530 °C, a ~20 % reduction of the Ge fraction was observed, which is due to intermixing of Si and Ge. This is consistent with our previous photoluminescence results, which revealed a significant blue shift of the Ge dot-related emission peak in this growth temperature range. The Ge concentration decreases more slowly when the growth temperature is increased above 600 °C, which can be explained by geometrical arguments. The longer distance between the interface and the core of these larger sized dome-shaped islands implies that less Si atoms reach the dot center. In general, the uncapped Ge dots have similar widths as the embedded islands, but the height is almost exclusively larger. Furthermore, the Ge concentration is slightly lower for the overgrown dots.
|
|
| 14. |
- Karim, Amir, 1976-, et al.
(författare)
-
Photoluminescence Studies of Sn Quantum Dots in Si Grown by MBE
- 2005
-
Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 27:5, s. 836-840
-
Tidskriftsartikel (refereegranskat)abstract
- A few nanometer thick SnxSi1−x layers with x 0.1 grown on silicon (1 0 0) surfaces can be used to form tin (α-Sn) quantum dots as a result of heat treatment of such structures up to 800 °C. These quantum dots with a well-defined shape are expected to be a candidate for obtaining a low-energy direct band gap structure in Si. Absorption measurements reported by Ragan et al. have shown the onset of absorption at 0.27 eV indicating that the MBE-grown α-Sn quantum dots could be used, e.g. in infrared detectors or emitters. We have performed low temperature photoluminescence (PL) studies of some of the structures produced in this first study and observed no emission peak near 0.27 eV. The PL spectra are instead characterised by a broadband emission in the range 0.7–1 eV. Furthermore there are narrow features that have previously been described as the 789 meV C–O band and 1018 meV W or I1 band. The broad emission at 0.7–1 eV is attributed to the presence of defects introduced by the grown layers, which have suppressed the emission peaks related to the substrate as well. We have also grown α-Sn quantum dot samples on Si (1 0 0) substrates with very low doping concentrations. These samples show PL spectra with Si-substrate related peaks and a relatively lower broad feature at 0.7–1 eV. However, no emission was observed near 0.27 eV.
|
|
| 15. |
- Karim, Amir, 1976-
(författare)
-
Si-based structures for light emission and detection
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efforts to improve the optical performance of the indirect bandgap semiconductor silicon (Si) has been a major subject of research in the field of Si photonics due to the promising applications of Si based light emitters and detectors for optical communication. With that motivation three different Si based material systems were investigated; Si:Er/O layered structures, SiGe quantum dots and SiSn nano structures, all grown using the technique of molecular beam epitaxy (MBE). The main focus of this work has been on Si:Er/O layers, which lead to fabrication of Si-based light emitting diodes (LED) emitting at 1.54 mm wavelength. The work on SiGe structures lead to the fabrication of near-infrared light detectors, whereas the SiSn structures have not shown any strong optical character.Studies include epitaxial growth, structural characterization, device processing, electrical and optical characterizations. Material characterization of Si:Er/O structures using analytical electron microscopy (AEM) revealed interesting results with identification of two different type of microstructures in these layers depending on the Er and O concentrations. Several Si:Er/O LEDs were fabricated with different Er and O concentrations and the optical characteristics were investigated in order to find the best doping levels of Er and O for efficient light emission. The electroluminescence measurements revealed a strong 1.54 mm emission from these devices due to the intra 4f shell transition of Er3+ from the excited state (4I13/2) to the ground state (4I15/2). Si:Er/O waveguide LEDs have also been grown on SOI wafers using the optimized structure parameters obtained from mode confinement simulations as well as the microstructure investigations. The Si:Er/O waveguide LEDs are aimed at fabricating a planar Si cavity with Bragg mirrors on both sides to obtain light amplification and realise an electrically pumped Si laser. A focused ion beam (FIB) instrument was used to fabricate the Bragg mirrors but initial attempts did not result in light amplification in our Si:Er/O waveguide cavities.SiGe quantum dots are well-known quantum structures which are formed in a selfassembled fashion from Si/SiGe layer structures with a variety of shapes, sizes and compositions depending mainly on parameters like growth temperature and layer thicknesses. Optical properties of SiGe quantum structures have been studied while there has been little knowledge about their composition. A detailed compositional investigation of different SiGe dots on a nanometer scale was performed using AEM. The results showed a large degree of interdiffusion in large quantum dots, which was consistent with the optical properties of these dots. Using a multiple stack of Ge quantum dots and SiGe quantum wells, MOSFET type photodetectors working at 1.3 – 1.55 mm wavelength have also been fabricated and characterized.Research on the SiSn system was mainly motivated by the possibility to obtain a direct bandgap transition in Si based material as it was predicted theoretically and experimentally observed in the related GeSn material system by other researchers. Structural and optical characterizations of SiSn nano structures were performed. Although the same SiSn nano structures exhibit a weak signature of optical absorption, low temperature photoluminescence measurements did not reveal any emission peaks related to the SiSn dots.
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
- Larsson, Mats, et al.
(författare)
-
Growth-temperature-dependent band alignment in Si/Ge quantum dots from photoluminescence spectroscopy
- 2006
-
Ingår i: Physical Review B. - 1098-0121 .- 1550-235X. ; 73:19, s. 195319-1--195319-7
-
Tidskriftsartikel (refereegranskat)abstract
- The present work is a photoluminescence study of Si-embedded Stranski-Krastanov Ge quantum dots. The value of the conduction band offset is a result of the magnitude of the tensile strain in the Si surrounding the compressive strained Ge dot. Due to the increased Si/Ge intermixing and reduced strain in the Si barrier, a reduction of the conduction band offset is observed at increased growth temperatures. The optical properties as derived from photoluminescence spectroscopy are correlated with structural properties obtained as a function of the growth temperature. High growth temperatures result in large Ge dots with low density due to the pronounced surface diffusion and Si/Ge intermixing. As confirmed by photoluminescence, the band gap of the Ge dots increases with increased growth temperature due to the higher degree of Si/Ge intermixing. The band alignment is of type II in these structures, but the occurrence of both spatially indirect and spatially direct transitions are confirmed in temperature-dependent photoluminescence measurements with varied excitation power conditions. An increasing temperature results in a gradual transition from the spatially indirect to the spatially direct recombination in the type-II band lineup, due to higher oscillator strength for the spatially direct transition combined with a higher population factor at higher temperatures.
|
|
| 19. |
- Larsson, Mats, et al.
(författare)
-
Reversed quantum-confined Stark effect and an asymmetric band alignment observed for type-II Si∕Ge quantum dots
- 2005
-
Ingår i: Physical Review B. - 1098-0121. ; 71:11, s. 113301-
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the quantum-confined Stark effect for spatially indirect transitions in Stranski-Krastanov grown type-II Si∕Ge quantum dots. A linear blueshift of the spatially indirect transition is observed at increasing electric field in contrast to the commonly observed redshift for type-I transitions. A shift of the emission-peak position and different quenching rates of the photoluminescence for p-i-n and n-i-p diodes at increased electric field and temperature indicate a deeper notch potential for electrons above the dot than below due to a strain-induced asymmetry in the band alignment.
|
|
| 20. |
- Luo, G, et al.
(författare)
-
Suppressing phosphorus diffusion in germanium by carbon incorporation
- 2005
-
Ingår i: Electronics Letters. - : Iet. - 0013-5194 .- 1350-911X. ; 41:24, s. 1354-1355
-
Tidskriftsartikel (refereegranskat)abstract
- A problem in the Ge MOSFET process is that the phosphor-us for n-type doping in Ge diffuses very fast. It is very difficult to form the shallow source/drain p-n junctions. It is reported, for the first time, that the phosphorus diffusion in Ge during activation (or annealing) can be suppressed effectively owing to carbon incorporation.
|
|
| 21. |
- Lynch, S.A., et al.
(författare)
-
Toward silicon-based lasers for terahertz sources
- 2006
-
Ingår i: IEEE Journal of Selected Topics in Quantum Electronics. - 1077-260X .- 1558-4542. ; 12:6, s. 1570-1577
-
Tidskriftsartikel (refereegranskat)abstract
- Producing an electrically pumped silicon-based laser at terahertz frequencies is gaining increased attention these days. This paper reviews the recent advances in the search for a silicon-based terahertz laser. Topics covered include resonant tunneling in p-type Si/SiGe, terahertz intersubband electroluminescence from quantum cascade structures, intersubband lifetime measurements in Si/SiGe quantum wells, enhanced optical guiding using buried suicide layers, and the potential for exploiting common impurity dopants in silicon such as boron and phosphorus to realize a terahertz laser. © 2006 IEEE.
|
|
| 22. |
|
|
| 23. |
- Pidgeon, CR, et al.
(författare)
-
Pump-probe measurement of lifetime engineering in SiGe quantum wells below the optical phonon energy
- 2005
-
Ingår i: Semiconductor Science and Technology. - 0268-1242 .- 1361-6641. ; 20:10, s. L50-L52
-
Tidskriftsartikel (refereegranskat)abstract
- We have directly determined with pump/probe spectroscopy the light hole (LH1) excited state lifetime for the lowest heavy hole to light hole intrawell subband transition (HH1-LH1) for three prototype samples of Si/SiGe strain-symmetrized multi-quantum well structures, designed to have the final LH1 state increasingly unconfined. The transition energy is below the optical phonon energy. We find that a decay time of 20 ps for sample 1 with a well width of 5.0 nm lengthens to 40 ps for sample 3 with a well width of 3.0 nm, in good agreement with the design. In addition, we have measured the lifetime for holes excited out of the well, from which we determine the lifetime for diagonal transitions (back into the well) to be of approx. several hundred picoseconds.
|
|
| 24. |
- Rauter, P., et al.
(författare)
-
Direct determination of ultrafast intersubband hole relaxation times in voltage biased SiGe quantum wells by a density matrix interpretation of femtosecond resolved photocurrent experiments
- 2007
-
Ingår i: New Journal of Physics. - : Institute of Physics (IoP) and Deutsche Physikalische Gesellschaft. - 1367-2630. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- We report the quantitative and direct determination of hole intersubband relaxation times in a voltage biased SiGe heterostructure using density matrix calculations applied to a four-level system in order to interpret photocurrent (PC) pump-pump experiments. One consistent set of parameters allows the simulation of two kinds of experiments, namely pump-pump photocurrent experiments at a free electron laser (wavelength 7.9 mu m) and the laser-power dependence of the PC signal. This strongly confirms the high reliability of these parameter values, of which the most interesting in respect to Si based quantum cascade laser development is the extracted heavy-hole relaxation time. The simulations show that this relaxation time directly determines the experimentally observed decay of the pump-pump photocurrent signal as a function of the delay time. For a heavy hole intersubband spacing of 160 meV, a value of 550 fs was obtained. The experimental method was further applied to determine the LH1-HH1 relaxation time of a second sample with a transition energy below the optical phonon energy. The observed relaxation time of 16 ps is consistent with the value found for the same structure by transmission pump-probe experiments.
|
|
| 25. |
- Shieh, Jia-Min, et al.
(författare)
-
Enhanced photoresponse of a metal-oxide-semiconductor photodetector with silicon nanocrystals embedded in the oxide layer
- 2007
-
Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 90:5
-
Tidskriftsartikel (refereegranskat)abstract
- The authors report a two-terminal metal-oxide-semiconductor photodetector for which light is absorbed in a capping layer of silicon nanocrystals embedded in a mesoporous silica matrix on p-type silicon substrates. Operated at reverse bias, enhanced photoresponse from 300 to 700 nm was observed. The highest optoelectronic conversion efficiency is as high as 200%. The enhancements were explained by a transistorlike mechanism, in which the inversion layer acts as the emitter and trapped positive charges in the mesoporous dielectric layer assist carrier injection from the inversion layer to the contact, such that the primary photocurrent could be amplified.
|
|
