Photothermoacoustic Transformation of a Kummer-Gaussian Light Beam in CdTe Semiconductor Sensor Structures
- PDF / 726,689 Bytes
- 5 Pages / 594 x 792 pts Page_size
- 65 Downloads / 222 Views
Journal of Applied Spectroscopy, Vol. 87, No. 4, September, 2020 (Russian Original Vol. 87, No. 4, July–August, 2020)
PHOTOTHERMOACOUSTIC TRANSFORMATION OF A KUMMER-GAUSSIAN LIGHT BEAM IN CdTe SEMICONDUCTOR SENSOR STRUCTURES** G. S. Mityurich,a* V. P. Veleshchuk,b S. S. Girgel,a E. V. Lebedeva,c A. I. Vlasenko,b and S. N. Levitskiyb
UDC 621.373.8;621.315.5
Laser photothermoacoustic transformation in sensor semiconductor structures was experimentally and theoretically investigated. An expression for a pressure pulse describing the evolution of an ultrasonic response excited by a nanosecond laser pulse with a Kummer-Gaussian intensity distribution was obtained. The possibility of effective control of photothermoacoustic transformation of laser pulses in semiconductor structures used for creating highly sensitive detectors of ionizing radiation was experimentally demonstrated. Keywords: photoacoustic spectroscopy, Kummer-Gaussian laser beams, Kummer function, energy dissipation, pulsed photoacoustic signal. Introduction. Powerful nanosecond laser pulses during irradiation of semiconductor structures can create conditions causing the charge carriers to deviate considerably from thermodynamic equilibrium. This is important for forming nanoand micron-sized subsurface layers in CdTe crystalline structures. CdTe doped with In is a promising material for ionizing radiation detectors because of the sharp rectifying properties of the structure, the small leakage current, and the ability to ensure complete separation and collection of charge carriers by a strong electric field in the diode. This enables conditions to be created for ultrahigh energy resolution in the detector. However, doping CdTe with In is accompanied by self-compensation, i.e., formation of oppositely charged intrinsic defects or complexation of the dopant. This limits the charge concentration to values substantially less than the dopant concentration. One of the most important problems is finding an effective doping method that allows the effect of self-compensation to be diminished. Such a method should provide a sharp In distribution profile and a small doping depth of the p–n-transition. The doping process should not destroy the defect structure and electrical properties in the crystal bulk. The use of laser pulses on semiconductor structures was shown to be promising for providing the above conditions [1]. Calculations. Narrowly controlled circular Kummer-Gaussian laser beams [2, 3], the amplitude of which can accurately be held constant, are rather effective in addition to Bessel light beams and can be written as [4] v
⎛ P ⎞ ⎛ R ⎞ E = G⎜ ⎟ ⎜ ⎟ ⎝ QB ⎠ ⎝ QB ⎠
m 1 F1
(−ν, m + 1, R ) e 2 2
im φ
,
(1)
⎛ R2 ⎞ 2 where G(R, Z) = 1 / QB exp ⎜⎜ i ⎟⎟ is a Gaussian; 1F1(–ν, m + 1, R2 ), a degenerate hypergeometric function often called a ⎝ QB ⎠ Kummer function; QB = Z – Q0, a dimensionless complex parameter of the light beam, Q0 = Qo′ + i Q0″ , a complex quantity; _____________________ *
To whom correspondence should be addressed.
**
Presented at "The
Data Loading...
