Piezocapacitance spectroscopy of a radiation defect in silicon

. In this article, using non-stationary capacitive deep-level spectroscopy (DLTS), the dependence of the parameters of the radiation defect with the ionization energy


Introduction
Uniaxial elastic deformation of cubic crystals can, under certain conditions, lead to a shift and splitting of the energy levels of anisotropic centres [1].The study of the dependence of the properties of the centres on the direction and magnitude of the pressure P provides significant additional information about the symmetry of these centres.Uniaxial deformation is widely used in the study of luminescence spectra, optical absorption, and electron paramagnetic resonance (EPR) of local centres.Capacitance spectroscopy methods [2,3] are used much less frequently to detect the effect of uniaxial pressure on the parameters of centres with deep levels (DL), although they are highly sensitive, allow one to determine the parameters of centres at their low concentration, and can be used to study centres of nonradiative recombination and non-paramagnetic centres.

E E eВ   
A-centre and E-centre from P using non-stationary capacitance spectroscopy DL (DLTS).

Samples and measurement methods
Samples for measurements were made from n Si  brand KEF-5 (specific resistance 5 .Om cm ) and had the shape of a parallelepiped with dimensions 6 1.5 and external pressure was applied along these directions.On the side faces, Schottky barriers were created by sputtering with gold and ohmic contacts.The DL parameters were determined using DLTS in the constant capacity mode by measuring the dependence of the level recharge time constant  on temperature T at different gating windows.The voltage across the diode was measured at times 1 2 1 , 3 t t t  from the beginning of the rectangular back mix pulse.

Piezocapacitance RD spectroscopy, A-centre and E-centre
Oriented deformation in combination with DLTS was used for the first time in [3].Options A-centre, we determined using DLTS in constant capacity mode.To determine the ionization energy A-centre (without deformation and with deformation after splitting) 1 t changed within 0.5 500 .ms  DLTS measurements were made immediately after irradiation.Irradiation was carried out at 300 К   -isotope quanta 60 Со with intensity 12 3.4 10  quantum/cm 2 up to a dose of the order 18 1 10  quantum/cm 2 .Large doses lead to diode base compensation and DLTS measurements become impossible.Immediately after irradiation, several peaks were observed in the spectrum (Fig. 1, curve 2) due to the charge exchange of DL with ionization energies of 0.17 (A-centre), 0.23 (B), 0.3 (C), 0.37 (D), 0.44 (E-centre) and 0.53 (K) from the bottom of the conduction band.A-cents had the maximum concentration   14 3 1.5 10 cm   .
Uniaxial deformation causes a noticeable splitting of the DLTS peak (Fig. 2).As can be seen from the figure, with increasing strain, the DLTS spectrum associated with the A centre begins to expand and the peak shifts towards lower temperatures.Starting from some deformation values for example, in the direction [100] P=0.394, and P=0.65GPa for [111], a splitting of the DLTS peak is observed.Table 1 shows the results of changes in the activation energy i Е  level of the A-centre under uniaxial deformation by pressure Р (in units / GPa meВ ) and compared with the results of [3].)In this work, we also studied the effect of uniaxial deformation in the [100], [110], and

Ф cm  
The measurements showed that, under the action of deformation, the position of the peak associated with E-centre, shifts towards lower T, but the sensitivity to strain in all cases studied was very low (Table 1).After annealing at 250 ℃ for 20 minutes, the sensitivity of the peak (corresponding E-centre) to deformation increases significantly.As can be seen from Table 1, our results agree satisfactorily with the data of [3].  10 cm  (Fig. 1, curve 1).Irradiation was carried out at 300 K  -isotope quanta 60 Со with intensity The nature of this centre is debatable; it may be an oxygen-divacancy complex [4].The splitting of the energy level of just this centre under the action of uniaxial compression was investigated.Before proceeding to the measurement of uniaxial compression, we studied the annealing kinetics of the levels L. The diodes were subjected to isothermal annealing at 250 ℃.The heat treatment process can be divided into two stages (Fig. 4).First stage annealing for 1 h.Level concentration L drops by about an order of magnitude.Upon further annealing (II stage) in the time interval

 
and the split levels have a fixed ionization energy.The values are determined from the Arrhenius lines i E and θ0. for all three directions of deformation (Table 2).The values thus calculated β for the A-centre and level L close to each other (Table 2), however, the symmetry of these two centres, apparently, is different.

Results and discussion
In article [5] from the dependence of resistivity, n Si  compensated A-centers, the average displacement of the level is determined from the deformation 0.17 to the day of the conduction zone.According to [5].The deformation coefficient β for the A-centre is small, especially in the direction [110] and β=0 in [111].Mapping to values β for impurity levels shows that for impurity centres β much less [6,7].
Piezocapacitance RD (A-centre) spectroscopy study showed that uniaxial deformation causes noticeable splitting of the DLTS peak A-centre.
The effect of uniaxial strain on the DLTS of the E centre in n-Si.It is shown that the peak corresponding to the E-centre retains its shape during deformation and shifts relatively weakly towards low energies.After annealing at 250 ℃ for 20 minutes, the sensitivity of the peak corresponding to the E centre to deformation increases significantly.
For the first time, using DLTS, the effect of uniaxial compression on the level parameters was studied.

[
111] directions in samples n-Si on the properties of the E-centre  

Fig. 2 .
Fig. 2. DLTS spectra of the A-center for different directions of uniaxial compression.
immediately after irradiation, several peaks were observed in the spectrum (Fig.1, curve 2) due to the charge exchange of DL.After measuring DLTS, the sample was annealed at 250 ℃ for 20 minutes.As a result of annealing, the concentrations of all RDs decrease (A centre from about new RD arises (level L in Fig.1, curve 3) with a concentration of the order

E3SFig. 3 .
Fig. 3. Dependencies     2 lg 1 / T f T  changes slowly.In two samples, the level concentration L during the entire annealing decreased synchronously (Fig. 4, curves 1, 2) Fig. 5a and 5b show the DLTS peaks due to level recharging L, at P=0 and under uniaxial compression along the [110], [111], and [110] axes.It can be seen from the figure that deformation leads to a significant change in the PD property and level splitting; the level is related to the anisotropic centre.The parameters of the split states were determined, as was related above, from the temperature dependence of the position of the peak maximum with varying strobing windows.The amplitude of the peaks practically did not depend on T. The measurement results are shown in Fig. 3.As can be seen from the figure, the experimental values θ(T) lie well on the Arrhenius lines, i.e.

E3SFig. 4 .Fig. 5 .
Fig. 4. Kinetics of changes in level concentrations L in two samples under isothermal annealing at 250 ℃ Quantum and annealing samples at 250 ℃ for 20 minutes.It was found that under the action of deformation the splitting of the level L. i E  depends on the crystallographic direction and reaches the values 0.06-0.12eB.

Table 2 .
Values determined i