Deep levels in silicon–oxygen superlattices Deep levels in silicon–oxygen superlattices (original) (raw)
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Physica status solidi, 2016
In this paper, the deep levels found by Deep-Level Transient Spectroscopy in Si-O superlattices on p-type silicon substrates are compared with the band of near mid-gap hole traps typically observed at the Si/SiO2 interface. In addition, the impact of a post-deposition Forming Gas Annealing is investigated. A large similarity between the two material systems is reported, which indicates that similar silicon-oxygen bonds may be responsible for the deep hole traps. TEM cross section of a two layer Si-O superlattice on a ptype silicon substrate.
Physica Status Solidi B-basic Solid State Physics, 2016
The presence of deep levels in a silicon-oxygen (Si-O) superlattice (SL) deposited on p-type silicon substrates has been investigated by deep-level transient spectroscopy (DLTS) on thermally evaporated Cr Schottky barriers (SBs). The SLs have been fabricated with different thicknesses of the silicon interlayers, formed by chemical vapor deposition. It is shown that a broad band of hole traps is present near the surface of the SB, which is associated with the SL. In addition, the activation energy corresponding with the peak maximum shifts to higher values with respect to the valence band and gives rise to a higher trap concentration with increasing silicon interlayer thickness. It is proposed that these states are associated with the structural defects found in similar SL structures, that is, with the epitaxial quality and not with the Si-O bonds in the atomic layers. The change in the DLT-spectra with silicon thickness could be related with the transformation of the structural defects from small selfinterstitial clusters to stacking faults.
Nanoscience and …, 2010
p-type 4H-SiC epitaxial layers grown by chemical vapor deposition have been implanted with 200 and 100 keV protons at five different implantation temperatures. An isochronal annealing series was performed from 100 to 1800°C, and Al-doped epitaxial layers have been characterized by means of deep level transient spectroscopy ͑DLTS͒ after each annealing step. DLTS measurements were carried out in the 150-670 K temperature range and revealed the presence of eight hole traps located in the 0.18-1.8 eV range above the valence band ͑E V ͒. Heat treatments for temperatures above 700°C showed the progressive reactivation of the Al doping in the implanted region, which is completed after a 1500°C annealing treatment. Two traps located at E V + 0.44 eV and E V + 1.8 eV are persistent even after annealing at 1800°C, while the other traps anneal out after heat treatments at ഛ1700°C. An activation energy for dissociation of 6.2 eV is estimated for the hole trap at E V + 0.79 eV, and the nature of this defect is discussed on the basis of previous experimental results and theoretical calculations. Furthermore, the study of the annealing behavior as a function of the implantation temperature shows that the detected traps display an increase of concentration for increasing implantation temperatures.
Quasi Two-Dimensional Si-O Superlattices: Atomically Controlled Growth and Electrical Properties
We perform a systematic study on the growth of epitaxial Silicon–Oxygen superlattices (SLs) and investigate the impact of structural properties on the electrical performance. Si layers and O atomic layers (ALs) are deposited using SiH 4 and O 3 reactions respectively. Although the deposition of O ALs and epitaxial Si thereon, i.e. 1 st period of Si–O SL is well documented, the controlled deposition in maintaining the overall crystalline quality of SL is still a challenge. This is due to inability to limit the O layer to sub-AL content (1AL = 6.7 × 10 14 at/cm 2) at higher periods (≥2). The Si surface prior to O AL deposition is chemically modified with H-passivation and sub-AL O-content is achieved. This ensures minimum structural distortions, enabling epitaxial ordering of Si and hence the epitaxial Si–O SL up to 5-periods. No SiO x clusters are detected and O layers are stable at Si deposition temperature. Electrically, donor defects increase with Si–O periods and partially reduced with forming gas anneal. The presence of defects and increased roughness during the growth, degrade the mobility due to coulomb and surface scattering respectively. It can be circumvented by optimizing SL parameters and other process integration parameters subjected for future research.
Spectroscopic observation of interface states of ultrathin silicon oxide
Journal of Applied Physics, 1996
Interface states in the Si band gap present at oxide/Si(100) interfaces for ∼3-nm-thick Pt/2.1∼3.6-nm-thick silicon oxide/n-Si(100) metal–oxide–semiconductor devices are investigated by measurements of x-ray photoelectron spectra under biases between the Pt layer and the Si substrate, and their energy distribution is obtained by analyzing the amount of the energy shift of the substrate Si 2p3/2 peak measured as a function of the bias voltage. All the interface states observed using this new technique have discrete energy levels, showing that they are due to defect states. For the oxide layer formed in H2SO4+H2O2, the interface states have three density maxima at ∼0.3, ∼0.5, and ∼0.7 eV above the valence-band maximum (VBM). For the oxide layer produced in HNO3, two density maxima appear at ∼0.3 and ∼0.7 eV above the VBM. The energy distribution for the oxide layer grown in HCl+H2O2 has one peak at ∼0.5 eV. The 0.5 eV interface state is attributed to the isolated Si dangling bond defe...
The first results are presented of a deep-level transient spectroscopy (OLTS) study of deep levels in p-type silicon wafers with different oxygen contents and thermal pretreatments. The OLTS results are correlated with those of a structural characterization using cross-sectional transmission electron microscopy (EM). The silicon oxide precipitate density and distribution correlates with the occurrence of minority carrier traps in the substrate. After irradiation with the fission products of a 2s2Cf source, an order of magnitude increase of the leakage current is obsewed. At the same time, new o m peaks are introduced. While the creation of the divacancy-related centre (VZ) is not affected by the presence and the status of oxygen, this is not the case for the second dominant peak related to an interstitial carbon-interstitial oxygen complex (CiOi) in p-type Czochralski substrates. In general the concentration of this trap scales with the residual interstitial oxygen content.
Silicon–O–M–O–silicon superlattice
Microelectronics Journal, 2006
The success of heterojunction quantum wells and quantum dots in III-Vs has not been extended to silicon because the ideal barrier, SiO 2 , is amorphous, preventing the formation of quantum structures with silicon. The possibility of a few monolayers of oxide inserted between adjacent silicon layers was proposed and realized with a superlattice (SL) structure consisting of Si-Si-O-Si-Si-Si, having a monolayer of oxygen in each period introduced by adsorption onto the 2 Â 1 reconstructed surface along the Si(1 0 0). Reduction of the period leads to a slight up-shift of the energy of the emitted light, indicating that the essential objective of boosting the optical transition by promoting direct transitions has not been realized. Annealing in H 2 +O 2 results in significant improvement in PL and EL, showing that specific defects, e.g., Si-O complexes may be responsible for the observed light emission. The role of Si-O complex being the origin of emission is further supported by the observation that the emission of visible light from polycrystalline Si and SiO 2 structure is similar to the epitaxial superlattice with oxygen. The computed strain in a new type of superlattices consisting of SiO 2 , and GeO 2 is much lower than the Si-O SL. The EL in Si-O superlattice with the use of a Schottky barrier to provide electron-hole accumulation allows double injection into states higher in energy than the bandgap of Si, a prerequisite for injection laser without the need to use a wide-band pn-junction. r
The electronic and optical properties of Si/SiO2 superlattices: role of confined and defect states
Surface Science, 2000
The Si layer thickness dependence of the optical properties of silicon/silicon dioxide (Si/SiO 2 ) superlattices has been, for the ®rst time, theoretically investigated. In our ®rst principle calculation we consider both fully passivated interfaces and the presence of oxygen vacancy at the interface. Our results show the key role played both by the quantum con®ned states and interface states in the experimentally observed visible luminescence in Si/SiO 2 con®ned systems. Ó