SU646795A1 - Method of determining parameters of a conductor - Google Patents

Description

The invention relates to semiconductor technology and can be used to determine the width of the forbidden zone, local energy levels, as well as on the basis of these data on the composition of the material, for example CdS, Se, x, Te, etc. The known method for determining the parameters of a semiconductor by the red boundary and impurity photoconductivity or optical absorption 1. However, in the absence of preliminary information from the band structure, the accuracy of this method is small due to the ambiguity and nonlinearity of the dependence of the absorption coefficient irradiating the energy-from the semiconductor light quanta h near red border. In addition, this method makes it impossible to determine the thermodynamically equilibrium values of the parameters: the so-called optical band gap and the optical ionization energy of the local level are fundamentally different from the corresponding equilibrium (thermal) parameters. There is also known a method of determining the parameters of a semiconductor, for example, the width of the forbidden zone and local energy levels in the forbidden zone, including 1). Electromagnetic semiconductor material irradiation. with quantum energy exceeding the width 3anpeii; eH-. NOI zones (2.) In this case, to determine the parameters, the features of the energy relaxation process of light carriers created by light are used, namely, the ionization processes of valenceHeJx, electrons and the breaks in the spectrum of the internal photoelectric effect associated with them. This method allows choosing the most convenient for the spectral region is independent of the width of the forbidden zone, but does not eliminate the above difficulties, the spectral dependence used in it is also ambiguous and the equilibrium parameters with its help determine The aim of the invention is to find thermodynamically equilibrium values of parameters and to increase the accuracy of determining parmeters.

This is due to the fact that the semiconductor is irradiated with single pulses of electromagnetic radiation with a duration greater than the relaxation time of the carrier energy, but less than the lifetime of the latter, and by increasing the popup temperature (during the pulse, determine the width of the forbidden zone and the level of local levels energy in the forbidden zone. The temperature rise of a semiconductor sample is measured first by irradiation, its pulse, the energy factor, the quantum b, and the number of quanta the sample's temperature when it was emitted by a pulse with a quantum energy and the number of quanta Jfj. The obtained results are presented as two points in the coordinate system dT / N, h, and the length of the section Cuts off on the –f axis by a straight line through the obtained points, The semiconductor parameters are determined.

The temperature rise of the sample of the conductor during the pulse dT is proportional to the thermal energy b, released during thermalization (lowering the energy to the average, corresponding to this temperature - 1.5 kT in a non-degenerate semiconductor) and non-radiative trapping to local levels of free electrons and holes created by light The energy of a quantum b is greater than the width of the reserved area of the E. This energy is connected with the limit e aA to the parameters by a simple linear relationship. Irradiation of a semiconductor sample. impulse (light c and duration ty exceeding the energy relaxation time (t 10 s), but shorter, H (|| resHy 11d1N1ig Carriers (both types when determining Irf, and one of the two when determining the local levels of levels)) and measuring dT allows you to find a value.

 The relationship between the value of Q (dT) and the parameters defined: the thermal width of the forbidden zone B and the energy position of the local levels, energy relative to that of the allowed; - zones in which the charge carriers have a longer lifetime (-Ed). The lifetime of the carriers in the zongis is indicated by t and t,, -leave

t ;.

When determining TSg, the pulse duration must satisfy the conditions of

 T, T

viyu

z

during the time of the impuls phase, only the thermalization energy is made in the sample::.

   Q.NCh --Eg-3kT).

 - - - - -.

ABOUT)

E h-P-Q / N-SkT

In determining E, the relation t, ty tj must be satisfied. Thermalization energy and energy of non-radiative capture of short-lived carriers, i.e. all air, are released in the sample during the time iy. gi of a pulse minus N (Yd + 1,5KT) of the capture energy of long-lived carriers emitted after the pulse

rn (b - Ud-1,5KT), from

: E h9-Q / H-1,5kTT (2)

The relationship between Q and dT is determined by the ratio QacfnftT where i is the heat capacity, a / l is the mass of that part of the sample where thermal energy is released. For convenience of measurements, one can take a sample in the form of a thin plane-parallel plate and measure the average temperature rise of the illuminated part of the plate dT. Then

(5 stdT, (3)

Do glo is the mass of the illuminated part of the plate, tinke (() p is the density, d is the thickness of the plate, S is the area of the light spot.

 -. d. lt-o1 f dT (x) o (x

 about : . , . .., ..

By measuring dT with 43), we find t Q, and then, depending on the ratio between me and ti / and t, tj, we determine either E by the formula (1),

or Un according to the formula (2).

In order to provide a sufficiently high sensitivity when measuring the pulse temperature rise, it is possible to use

The spectral dependence of the spectrum of any optical characteristic of the sample, for example, absorption, reflection, and luminescence. If the sample is in the form of a thin plane-parallel plate, it is sufficient to measure the neutral shift of the transmission edge of the sample. Since the change in the potlshtsen ratio of the sample is about ((drs) directly proportional to dT, and

DOS when measuring the transmission of the plate, ki is compounded in the same way as d.T, (AiSk. D JjAcA K) dx) ;, the experimentally measured shift of the transmission edge is proportional to the average rotation of the:

peratura illuminated part of the sample.

The temperature coefficient required for such a method to be determined with the displacement kj rf is associated with: the coefficient of the coefficient; the coefficient of the forbidden width and for the length of

semiconductors are known.

Claims (2)

Due to the linear relationship between dT, b and the measured energy pargillet Gum of the semiconductor V ErfME, measurements and calculations are significantly reduced and their accuracy is increased. By irradiating the semiconductor in series with two pulses of the same duration, but different energy of quanta hO, we measure the corresponding temperature increases dT, 2 I proportional to the energies C, and 2 Presenting the results of measurements in the form of two points in the coordinate system АТ / к, hJ and a straight line through these points, we find h-, (the intersection point of with the axis of energy), whence we directly obtain AND, if ALL ε, t ,, from formula (1). Taking into account that h%) corresponds to Q 0, we have Erf h-; o-3kT. CA at f, -: ty: tr2, if H0 corresponds to Q 0, we find from formula (2):: l, SkT In this case, to determine the parameters of the semiconductor, it is not necessary to make absolute measurements to measure dT with accuracy to a constant factor: the magnitude of this multiplier does not affect the value. The magnitude of absorbed quanta can be measured by photoconductivity; it is also sufficient to determine M | and N up to a constant multiplier. So, for example, to determine the width of the band gap from the thermally heated heating, a silicon wafer with a thickness of 3-10 cm is illuminated with a light pulse of duration t si s, the light spot is 4-10 cm. So KaKT-jofjii, the condition t that is necessary for determining Erf is fulfilled. .. The number of absorbed quanta N 7-Yu-, average, quantum energy h2, 6 eV. The edge of the optical gap, Kani, measured using the same light pulses, is shifted to the long wavelength region by 3 10 10, which at a temperature coefficient of E to 4-10 eV / deg gives an average temperature increase of dT 7.5, Using the ratio Gj-stdT, . with 0.181 cal / g hail and, -) 2.33 g / cm, we have Q 1, N S 2,310-J “1.43 eV. Further, 95 from (1) we obtain Eef - h t3 / N-3kT (2.6-1.43-0.08) e 1.09 EV. Claim 1. Method of determining the parameters of a semiconductor, such as the width of the forbidden zone and local energy levels in the overpriced zone, includes the irradiation of the semiconductor material with electromagnetic radiation with an energy of quanta greater than the width of the forbidden zone. Characterized by the fact that in order to find thermodynamically equilibrium napau ierpOB values, a semiconductor is irradiated with a single pulse of electromagnetic radiation with a duration greater than the relaxation time of the carrier energy, but less than the time of the latter, and the width of the forbidden zone is determined by increasing the temperature of the semiconductor during the pulse. and the position of local energy levels in the forbidden zone. 2. A method according to claim 1 / characterized in that, in order to increase the accuracy of determining the parameters, the temperature rise dT of a sample of a semiconductor is measured first by irradiating it with a pulse with a quantum energy hi and the number of quanta H, then the temperature rise of the sample is measured, by irradiating it with a pulse with an energy of ta quantum V h and the number of quanta M j, the results obtained are. in the form of two points in the coordinate system LT / H, h and the size of the segment, cut off on the axis b) by a straight line through the obtained points, determine the parameters of the semiconductor. Sources of information taken into account in the examination. 1. Kovtoshok and. F. Kontsevoy Yu.A. Measurement of parameters of semiconductor materials, M., Metallurgi, 1970, p. 402-405. 2. USSR author's certificate No. 405057, cl. G-01 N 21/00, 1974.