Truly ohmic contacts in engineered Al/Si/InGaAs(001) diodes (original) (raw)
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Electronics Letters, 1988
the spectral response of a GexSi1_x/Si strained layer alloy photodiode with a Ge content of 0•6. Both spectra are cor rected for the optical response of the monochromator and illumination optics. Because of differences in superlattice geometry and coupling efficiency, it is not possible to compare the quantum efficiency of the zone-folded detector accurately to that of the alloy photodetector. To compare the spectral response of the two devices, the spectra have been scaled to the same maximum amplitude. Although the macroscopic structure of the waveguide region is similar in both devices, it can be seen that the Geo. 6 Sio.4/Si detector, which relies only on the indirect bandgap at '•7 !lm for absorption, has a pho toresponse that is enhanced toward the infra-red relative to the superlattice device. The superlattice detector takes advan tage of both the indirect bandgap of the material at 1 ' 6!lm as well as new zone-folded gaps which occur at higher energyY Calculated transition energies for the (4 : 4) superlattice struc ture occur near 0• 75 and 1•0eV at room temperature.9 The bandgap for the Geo.6Sio.4 random alloy occurs at a slightly lower value of O•70eV.14 The difference between these two numbers is related in part to states in the valence band gener ated by the Kronig-Penney periodic potential present in the superlattice but not in the random alloy. The superlattice structure and the random alloy region have similar thick nesses and are surrounded by Si on each side. Both structures are therefore subject to an additional quantum confinement factor which increases further the fundamental bandgap by about the same amount in both cases. It appears, therefore, that the Kronig-Penney superlattice potential may help to skew the spectral response of the superlaUice toward high energies compared to the response of a random alloy of similar average composition. A more precise comparison between the strained super lattice and strained alloy detectors is not possible at present because of the difficulty associated with determining the actual equivalent alloy composition for the superlattice region. This difficulty has its origin in the finite thickness of the super lattice layers. In the specific case of the (4 : 4) superlattice used in our experiments, the superlattice consists of five repetitions of the GeSi (4: 4) unit. However, the last Si layer is adjacent to the Si buffer layer and indistinguishable from it. Therefore, the quantum well consists of five Ge regions and four Si regions. This means that the average composition is Ge-rich relative to a Geo.,Sio. , aIloy. On the other hand, the effective composition is probably Si-rich compared to the Geo. 6 Sio'4 alloy composition used for comparison in this work. In conclusion, photodiode detectors have been fabricated from GeSi (4 : 4) atomic strained layer superlattices. The elec trical characteristics of these photodiodes show the presence of a substantial component of generation-recombination current which may be related to the 80 heterointerfaces in the device structure. The superlattice structure extends the optical response of Si from '•0 to 1• 3 Jim.
Andreev reflection in engineered Al/Si/In x Ga 1−x As(001) junctions
Philosophical Magazine Part B, 2000
Complete suppression of the native n-type Schottky barrier is demonstrated in Al/InGaAs(001) junctions grown by molecular-beam-epitaxy. This result was achieved by the insertion of Si bilayers at the metal-semiconductor interface allowing the realization of truly Ohmic non-alloyed contacts in lowdoped and low-In content InGaAs/Si/Al junctions. It is shown that this technique is ideally suited for the fabrication of high-transparency superconductorsemiconductor junctions. To this end magnetotransport characterization of Al/Si/InGaAs low-n-doped single junctions below the Al critical temperature is presented. Our measurements show Andreev-reflection dominated transport corresponding to junction transparency close to the theoretical limit due to Fermi-velocity mismatch.
Tuning of Schottky barrier height of Al/n-Si by electron beam irradiation
Applied Surface Science, 2017
Highlights Tuning of Schottky barrier height can be achieved by electron beam irradiation at different doses on n-Si wafer prior to the fabrication of Schottky contact. The XPS analyses have shown irradiation induced defects and the formation of several localized chemical states in Si/SiOx interface that influences the Schottky barrier height. The thickness of the SiOx layer at the surface calculated from the intensities of XPS Si2p spectra and found to decrease with increase in the dose of electron beam irradiation. High ideality factor indicates metal-insulator-semiconductor configuration of the Schottky diode and the inhomogeneous nature of the Schottky barrier height. The Schottky barrier inhomogeneity decreases with increase in dose of electron beam radiation. The modifications in I-V characteristics as a function of electron dose is caused due to changes in the Schottky diode parameters and different transport mechanisms, such as space charge limited emission and tunneling through the trap states that are competing with the thermionic emission of electron.
A study of Al/Si3N4/ultrathin Si/GaAs structures by DLTS and C–V measurements
Thin Solid Films, 2003
We present a study on electrical properties of AlySi N ySiyGaAs structure studied by deep level transient spectroscopy and 3 4 capacitance-voltage technique. Here, the Si means an ultrathin silicon layer with thickness of approximately 2 nm. We have modelled the presented structure, while emissions from deep levels at SiyGaAs interface, traps in the bulk of GaAs and from a quantum well (QW) possibly formed by the Si interlayer, were taken into the account. Four deep traps were identified in the structure with the following thermal activation energies: 0.04, 0.19, 0.40 and 0.68 eV. The energy levels 0.4 and 0.68 are related with As defects, while the energy levels 0.04 and 0.19 are associated with the presence of the Si interlayer. Based on the emission behaviour, an existence of the QW is not probable (can be excluded). Rather, parameters of the Si-related energy levels suggest the levels are induced by d-doping of GaAs. ᮊ
Modification of Al/GaAs(001) Schottky barriers by means of heterovalent interface layers
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1994
The Schottky barrier height in AI/Si/GaAs(OOI) junctions grown by molecular-beam epitaxy was determined in situ by means of x-ray photoemission spectroscopy and ex situ through currentvoltage and capacitance-voltage measurements. We found that the barrier height can be tuned from a minimum value of 0.2 eV to a maximum of 1.1 eV provided that a sufficiently high As or Al flux is employed during the growth of the Si interface layer. The minimum and maximum values of the barrier are already established for Si layer thicknesses in the 1-2 monolayer range. We propose that the changes in barrier height derive from the establishment of a Si-induced local interface dipole. The magnitude and orientation of the dipole reflects the detail of the atomic reconstruction achieved at the interface in the different growth conditions.
Journal of Applied Physics, 2010
The forward bias current-voltage ͑I-V͒ characteristics of Au/n-Si Schottky barrier diodes ͑SBDs͒ with Zn doped poly͑vinyl alcohol͒ ͑PVA:Zn͒ interfacial layer have been investigated in the wide temperature range of 80-400 K. The conventional Richardson plot of the ln͑I o / T 2 ͒ versus q / kT has two linear regions: the first region ͑200-400 K͒ and the second region ͑80-170 K͒. The values of activation energy ͑E a ͒ and Richardson constant ͑A ء ͒ were obtained from this plot and especially the values of A ء are much lower than the known theoretical value for n-type Si. Also the value of E a is almost equal to the half of the band gap energy of Si. Therefore, the ⌽ ap versus q / 2kT plot was drawn to obtain the evidence of a Gaussian distribution ͑GD͒ of barrier heights ͑BHs͒ and it shows two linear region similar to ln͑I o ͒ / T 2 versus q / kT plot. The analysis of I-V data based on thermionic emission of the Au/PVA:Zn/n-Si SBDs has revealed the existence of double GD with mean BH values ͑⌽ B0 ͒ of 1.06 eV and 0.86 eV with standard deviation ͑͒ of 0.110 eV and 0.087 V, respectively. Thus, we modified ln͑I o / T 2 ͒ − ͑q͒ 2 / 2͑kT͒ 2 versus q / kT plot for two temperature regions ͑200-400 K and 80-170 K͒ and it gives renewed mean BHs ⌽ B0 values as 1.06 eV and 0.85 eV with Richardson constant ͑A ء ͒ values 121 A / cm 2 K 2 and 80.4 A / cm 2 K 2 , respectively. This obtained value of A ء = 121 A / cm 2 K 2 is very close to the known theoretical value of 120 A / cm 2 K 2 for n-type Si.
Barrier height inhomogeneities of epitaxial CoSi2 Schottky contacts on n-Si (100) and (111)
Solid-State Electronics, 2000
The forward current±voltage characteristics of epitaxial CoSi 2 contacts grown by Ti-interlayer mediated epitaxy (TIME) scheme on n-type Si substrates of both and orientations are studied in the temperature range from 80 to 300 K. At high temperatures (>220 K), the I±V characteristics obey the ideal thermionic emission model. The Schottky barrier heights stay H0.61 eV and the ideality factors are close to unity. At low temperatures, a change in the characteristics is observed around 10 À4 A/cm 2 , which is more signi®cant for the contacts on Si (111) than for those on Si (100). Above this current, the I±V curves can also be ®tted by the equation based on the thermionic emission theory, but the apparent barrier heights decrease and the ideality factors increase with decreasing temperature. This abnormal behavior, as well as the curved Richardson plots, are interpreted by the assumption of a Gaussian distribution of barrier heights, which is in agreement with the statistical distribution obtained directly from ballistic electron emission microscopy (BEEM) measurements. The excess current at small bias region is explained by coexistence of some small patches of reduced barrier height with the pinch-o model. The CoSi 2 contacts on Si (111) contain more patches with larger parameter values than those on Si (100), which causes a signi®cant dierence in the I±V characteristics at low temperature. 7
Silicon L2,3 core absorption obtained at the buried Al/Si(111) interface
Physical review. B, Condensed matter, 1991
Silicon L2 3 absorption spectra are obtained by spatially resolved electron-energy-loss spectroscopy as a function of distance away from the buried Al/Si(111) interface. Within 0.6 nm, scattering below the bulk absorption threshold is observed, accompanied by changes in shape above the threshold. In silicon, where the core hole is well screened, these variations signify changes in the local density of states above and below the conduction-band edge on a scale of about 0.3 eV. The results are discussed within the framework of the metal-induced-gap-states model. During the past ten years there has been considerable progress towards understanding the formation of a Schottky barrier at the metal-semiconductor interface. ' An atomistic verification of this understanding has been lacking, however, because a microscopic probe for local electronic properties has not existed for the fully formed interface. Recently, scanning-tunnelingmicroscopy studies have begun to address this problem with promising results. Spatially resolved electron-energy-loss scattering 5556 Qc1991 The American Physical Society