Adjustment of Terahertz Properties Assigned to the First Lowest Transition of (<i>D</i>⁺, <i>X</i>) Excitonic Complex in a Single Spherical Quantum Dot Using Temperature and Pressure

• Main Authors: Noreddine Aghoutane, Laura M. Pérez, Anton Tiutiunnyk, David Laroze, Sotirios Baskoutas, Francis Dujardin, Abdelouahad El Fatimy, Mohamed El-Yadri, El Mustapha Feddi
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Applied Sciences
• Subjects: terahertz properties; quantum dots; (<i>D</i>⁺, <i>X</i>) complex; temperature; pressure
• Online Access: https://www.mdpi.com/2076-3417/11/13/5969

This theoretical study is devoted to the effects of pressure and temperature on the optoelectronic properties assigned to the first lowest transition of the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><msup><mi>D</mi><mo>+</mo></msup><mo>,</mo><mi>X</mi><mo>)</mo></mrow></semantics></math></inline-formula> excitonic complex (exciton-ionized donor) inside a single <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>A</mi><mi>l</mi><mi>A</mi><mi>s</mi><mo>/</mo><mi>G</mi><mi>a</mi><mi>A</mi><mi>s</mi><mo>/</mo><mi>A</mi><mi>l</mi><mi>A</mi><mi>s</mi></mrow></semantics></math></inline-formula> spherical quantum dot. Calculations are performed within the effective mass approximation theory using the variational method. Optical absorption and refractive index as function of the degree of confinement, pressure, and temperature are investigated. Numerical calculation shows that the pressure favors the electron-hole and electron-ionized donor attractions which leads to an enhancement of the binding energy, while an increasing of the temperature tends to reduce it. Our investigations show also that the resonant peaks of the absorption coefficient and the refractive index are located in the terahertz region and they undergo a shift to higher (lower) therahertz frequencies when the pressure (temperature) increases. The opposite effects caused by temperature and pressure have great practical importance because they offer an alternative approach for the adjustment and the control of the optical frequencies resulting from the transition between the fundamental and the first excited state of exciton bound to an ionized dopant. The comparison of the optical properties of exciton, impurity and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><msup><mi>D</mi><mo>+</mo></msup><mo>,</mo><mi>X</mi><mo>)</mo></mrow></semantics></math></inline-formula> facilitates the experimental identification of these transitions which are often close. Our investigation shows that the optical responses of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>(</mo><msup><mi>D</mi><mo>+</mo></msup><mo>,</mo><mi>X</mi><mo>)</mo></mrow></semantics></math></inline-formula> are located between the exciton (high energy region) and donor impurity (low energy region) peaks. The whole of these conclusions may lead to the novel light detector or source of terahertz range.