J.H. Evans-Freeman

High resolution Laplace Deep Level Transient Spectroscopy studies of shallow and deep levels in n-GaN

Deep Level Transient Spectroscopy (DLTS) and high resolution Laplace DLTS (LDLTS) have been used to distinguish the difference between electrically active point and extended defects in MOVPE-grown n-type GaN. Three dominant features are observed in the conventional DLTS spectrum, with energies in the region of 40 meV, 550 meV and 1.46 eV. However, detailed examination with LDLTS shows that all these peaks consist of multiple emission rates. The low energy feature consists of three point defects closely spaced in energy, which are identified as ON, and SiGa. The feature at around 550 meV is shown to be due to defects in the strain field of a dislocation, which is deduced because the activation energy is dependent upon DLTS fill pulse length. LDLTS of this peak shows a very complicated spectrum, also indicative of a system of defects in a dislocation strain field. When applied to the very deep level of 1.46 eV, LDLTS shows multiple emission rates but they behave as point-defect like states.

High resolution deep level transient spectroscopy applied to extended defects in silicon

Deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS (LDLTS) have been applied to p-type Czochralski silicon that contains dislocations that have and that have not been locked by oxygen. The stress-induced dislocations have been immobilized by oxygen during heat treatment, which prohibits glide under certain applied shear stresses. The DLTS spectra show typical broad features between 100 and 320 K, characteristic of those seen in other dislocated silicon reported in the literature, and several components are present in the LDLTS spectra. In addition, DLTS spectra show a sharp narrow peak at 40 K at a rate window of 200 s-1 in the case of the locked dislocations, but not in the case of the sample where there is no oxygen locking. LDLTS shows that this deep level consists of more than one component and it is proposed that this peak is likely to be due to electrical activity associated with oxygen at the dislocation core. For hole emission at temperatures above 100 K, in the sample with unlocked dislocations, LDLTS detects a change of the emission rate of the carriers from some, but not all, of the components of the broad peak when the LDLTS fill pulse length is changed. This change is ascribed to band edge modification as the electronic states associated with the dislocation charge up during the fill pulse, and causes local electric field-driven emission of trapped charge during the reverse bias phase of the measurement. The LDLTS features which remain constant with fill pulse are proposed to be due to point defects in the material, which are not physically near dislocations.

High resolution Deep Level Transient Spectroscopy of p-n diodes formed from p-type polycrystalline diamond on n-type silicon.

High resolution Laplace deep level transient spectroscopy (LDLTS) at temperatures up to 450 K has been applied to thin polycrystalline semiconducting diamond films deposited on n-type silicon. Such structures form p-n diodes and can be characterised by capacitance DLTS. The boron doped diamond films were grown by hot filament chemical vapour deposition and the diamond film thickness was 3-4 microns. The boron concentration in the diamond films ranged from 7times1018 cm-3 to 1times1019 cm-3. In the LDLTS an isothermal measurement of thousands of capacitance transients was made and then averaged, and the result was inverse transformed to find the trap emission rate. The temperature was chosen as the maximum of the conventional DLTS emission peak. Conventional DLTS showed a combination of majority and minority carrier emission from deep levels. Multiple peaks in the LDLTS spectra suggest that some of the defects are located in a strain field. Capture cross section measurements also show that these peaks exhibit a time dependent capture cross section, which is indicative of carriers being trapped at a large electrically active defect. It is shown in the paper that a combination of LDLTS and direct capture cross section measurements can be applied to semiconducting diamond and can be used to understand whether defects possess single or multiple energy levels, and whether the trapping is at an isolated point defect or in defects in the strain field of an extended defect.

Laplace Deep Level Transient Spectroscopy of ultra shallow implanted junctions in Si

Deep level transient spectroscopy (DLTS) and laplace DLTS (LDLTS) measurements have been carried out on very shallow implanted p-n junctions in Si. Lightly doped n or p type Si was implanted with high doses at low energy of B or As, followed by implants of lower doses at higher energies of n or p dopants respectively, to simulate a doping well. The double implants resulted in p+/n/n- or n+/p/p- structures, which calculation showed had two depletion regions, one at the end of range of each implanted region. The electric fields in the two depletion regions act in the opposite sense, and by selecting the correct bias conditions it was possible to measure DLTS at the end-of-range of the two implanted regions. DLTS of the n+/p diodes displayed a high temperature peak due to the end of range of the shallow As implant, together with a defect originating much deeper behind the surface observed at low temperatures. LDLTS of the defect in the end-of-range of the As implant revealed two closely spaced energy levels, indicative of a complex defect structure in this region. The DLTS also showed a minority emission peak in all of the p+/n/n- and n+/p/p- samples. Their emission rate in LDLTS did not change with measurement temperature, and is discussed in terms of a small region at the shallow junction that is efficiently confining carriers.

Deep Level Transient Spectroscopy of Ultra Shallow Junctions in Si Formed by Implantation

We have carried out DLTS in highly doped p+n Ultra Shallow Junctions (USJ) in Si formed by ion implantation. The samples were implanted either with a 10keV or a 5keV B implant at a dose of 5*1015cm15. The 10keV sample was also implanted with P and the 5keV samples were implanted with P and increasing doses of As to simulate an USJ in an n-well. Due to the high P and/or As implant doses, it was observed that a band offset also exists between the n-type implanted region and the n-type starting material. Therefore these samples contain another depletion region apart from the expected p+n depletion region. However, the electric fields in these regions act in opposite directions assisting the profiling of different regions after careful selection of biasing conditions. A deep state is observed in the n-type region at EC-0.34eV which has a complex Laplace DLTS signature, which has arisen due to the implantation process.

High Resolution Deep Level Transient Spectroscopy of Hydrogen Interactions with Ion Implantation-Induced Defects in Silicon

We have investigated the difference between hydrogenated proton-ir radiated silicon, and ion-implanted silicon using high resolution Laplace Deep Level Tra nsient Spectroscopy (LDLTS). CZ silicon was irradiated with high-energy protons, to en sure that the irradiating particles passed through the samples, or implanted with very low dose s of ions. The ions used in the study were silicon, germanium and erbium. Doses were in the re gion of 10cm to minimise deep state assisted carrier removal, and the implantation depths we re of the order of 1-2microns. Hydrogen was introduced into the samples by either wet chemica l et hing or by inserting the samples into a hydrogen plasma. When hydrogen was introduced into t he proton or electron irradiated silicon, the vacancy-oxygen centre (VO) concentration reduced, and a level due to the vacancy-oxygen-hydrogen defect, VOH, appeared. When H is introduced into the ion-implanted samples, the appearance of VOH depends upon the implanted ion mass. As the mass increases the concentration of VOH reduces until it is not apparent when very heav y ions are implanted. We use this as a test of the presence of VO in the ion-implanted samples.