Resolution Deep Level Transient Spectroscopy Research Articles

High resolution deep level transient spectroscopy applied to extended defects insilicon

Deep level transient spectroscopy (DLTS) and high resolution Laplace DLTS (LDLTS) havebeen applied to p-type Czochralski silicon that contains dislocations that have andthat have not been locked by oxygen. The stress-induced dislocations have beenimmobilized by oxygen during heat treatment, which prohibits glide under certainapplied shear stresses. The DLTS spectra show typical broad features between100 and 320 K, characteristic of those seen in other dislocated silicon reportedin the literature, and several components are present in the LDLTS spectra. Inaddition, DLTS spectra show a sharp narrow peak at 40 K at a rate window of200 s−1 in the case of the locked dislocations, but not in the case of the sample where there isno oxygen locking. LDLTS shows that this deep level consists of more than onecomponent and it is proposed that this peak is likely to be due to electrical activityassociated with oxygen at the dislocation core. For hole emission at temperaturesabove 100 K, in the sample with unlocked dislocations, LDLTS detects a changeof the emission rate of the carriers from some, but not all, of the componentsof the broad peak when the LDLTS fill pulse length is changed. This change isascribed to band edge modification as the electronic states associated with thedislocation charge up during the fill pulse, and causes local electric field-drivenemission of trapped charge during the reverse bias phase of the measurement.The LDLTS features which remain constant with fill pulse are proposed to bedue to point defects in the material, which are not physically near dislocations.

High resolution deep level transient spectroscopy and process-induced defects in silicon

High resolution, or Laplace, deep level transient spectroscopy (LDLTS) enables the identification of very closely spaced energetic levels in a semiconductor bandgap. DLTS may resolve peaks with a separation of tens of electron volts, but LDLTS can resolve defect energy separations as low as a few MeV. In this paper, we present results from LDLTS applied to ion implantation-induced defects in silicon, with particular emphasis on characterisation of end-of-range interstitial type defects. Silicon was implanted with a variety of ions from mass 28 to 166. A combination of LDLTS and direct capture cross-section measurements was employed to show that electrically active small extended defects were present in the as-implanted samples. Larger dislocations were then generated in Si by oxygenation to act as a control sample. These stacking faults had typical lengths of microns, and their electrical activity was subsequently characterised by LDLTS. This was to establish the sensitivity of LDLTS to defects whose carrier capture is characterised by a non-exponential filling process and an evolving band structure as carrier capture proceeds. The LDLTS spectra show several components in capacitance transients originating from both the end-of-range defects, and the stacking faults, and also clearly show that the carrier emission rates reduce as these extended defects fill with carriers. The end-of-range defects and the stacking faults are shown to have the same electrical behaviour.

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

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

High resolution deep level transient spectroscopy studies of the vacancy-oxygen and related defects in ion-implanted silicon

We have carried out high resolution Laplace deep level transient Spectroscopy (DLTS) and conventional DLTS on silicon implanted with very low doses of either silicon, germanium, erbium, or ytterbium, and compared the results to those from electron-irradiated silicon. DLTS spectra of all the samples initially look very similar, and a peak at 95 K appears in all spectra which may be due to the vacancy-oxygen (VO) defect. We have carried out detailed measurements of the capture cross section and activation energy of this defect using Laplace DLTS. We show that, when the mass of the implanted ion exceeds that of silicon, the defect has a much smaller electron capture cross section than that expected for the VO defect, and a smaller activation energy. Hydrogen has been introduced, either by wet chemical processing or plasma, to all samples to observe the hydrogen–VO interactions resulting in VOH. By using high resolution DLTS we are able to establish that, after hydrogenation, the VOH defect exists with an identical emission rate in the silicon-implanted silicon and the electron-irradiated silicon, but not in the silicon implanted with heavier ions. We conclude that the peak at 95 K in the DLTS spectra in the case of the heavier ions is due to a different defect, confirming earlier reports in the literature. This defect is negatively charged, unlike VO, which is acceptor-like. We are also able to observe VOH in samples where VO is not present, after these samples have been annealed. We attribute this to release of V and H atoms from other defects during annealing.

Deep levels in MOCVD n-type hexagonal gallium nitride studied by high resolution deep level transient spectroscopy

Deep level transient spectroscopy (DLTS) is performed in MOCVD α-GaN either doped with two different concentrations of Si or unintentionally doped. Capacitance transients are measured in Schottky diodes made of an Au or Ni rectifying contact and an Al/Ti ohmic contact, both on the top of the samples. Only two peaks are detected in each sample in the energy range from the conduction band edge down to 1.1 eV below it, respectively close to 0.50 and 0.92–1.05 eV, by Fourier Transform DLTS (FTDLTS) with concentrations not exceeding 3×10 15 cm −3. These two results testify the high crystalline quality of the samples. The deeper level characteristics depend on the shallow impurity, either Si or the unintentional shallow donor, in deep states which comprise in fact a fine structure not evidenced by FTDLTS. A high resolution DLTS (HRDLTS) method is implemented to resolve this fine structure into several sub-levels which cannot be related to distinct chemical environments. The study of emission and capture kinetics confirms that at least three charge states (+,0,-) are involved. It is concluded that MOCVD α-GaN comprises deep centers which are stabilized in such a form with a concentration in the range of a few 10 14–10 15 cm −3.

Vacancy-related defects in ion implanted and electron irradiated silicon

We have studied self-implants in Czochralski n-type silicon and compared the resulting defect states with electron irradiated material and silicon implanted with heavy ions. Using high resolution deep level transient spectroscopy, we have been able to characterize the deep energy levels of the defects produced with a resolution of more than an order of magnitude better than previously published results. We have separated and characterized the various components of the peak associated with the acceptor (−/0) charge state of the divacancy at Ec −0.43 eV. There are very clear differences in these components among the materials studied.