Russian Physics Journal, Vol. 61, No. 2, June, 2018 (Russian Original No. 2, February, 2018)
CAPTURE AND EMISSION OF CHARGE CARRIERS BY
V. N. Davydov and O. A. Karankevich UDC 621.315.82.2
The interaction of electrons from the conduction band of the barrier layer of a LED heterostructure with the
quantum well size-quantization level described by the capture time and emission time of charge carriers is
considered. Relaxation of an excess energy upon capture and emission of charge carriers occurs as a result of
their collisions with phonons of the quantum well substance and the “barrier layer-quantum well” interface.
Analytical expressions are obtained for the interaction times, taking into account the depth of the size-
quantization level, involved in the interaction with electrons, and the width of the well. Numerical estimates
show that in real conditions, the capture time is shorter than the emission time, and this difference increases
with increasing depth of the level. At shallow depths, the capture and emission times are comparable.
Keywords: quantum well, capture time, emission time of charge carriers.
An important parameter of LED heterostructures (HS) with multiple quantum wells (MQW), which determines
the efficiency of the electrical energy conversion into the light energy, is the time of capture of free carriers by
a quantum well (QW). Knowledge of this parameter is necessary both for the understanding the picture of the injection
current formation in HSs with MQWs and for the formulation of conditions for increasing the power of optical
radiation. At present, there are papers [1–4], in which a technique is proposed for calculating the rate of the electron
capture by a QW in the sources of coherent radiation, in which a quantum well is the active region. The technique is
based on the calculation of this parameter from the experimental dependences of the laser threshold current. However,
in analytical calculations of properties of LED HSs with MQWs, this method of estimating the capture efficiency
cannot be used, since it does not give an analytical expression not only for the capture rate, but also for any parameter
directly related to the capture of carriers by a QW.
Moreover, in real heterostructures, the process of the charge carrier capture by a QW is always accompanied by
an inverse process – the emission of the previously captured carriers from the well into the barrier layer, which leads to
a decrease in the injection current in QW, and therefore, reduces the light power emitted by a HS. Despite the
importance of this parameter for the evaluation of the output characteristics of the coherent and incoherent radiation
sources, there are practically no works containing detailed analysis of the emission time of carriers from QW.
Consequently, consideration of the electron emission processes from QW is useful not only for a more complete
understanding of the current transfer in HSs with MQWs, but also, in particular, to elucidate the reasons for the
decrease in the luminescence efficiency of heterostructures at large forward biases [5–12].
The aim of this paper is to construct a physical picture of the capture and emission of charge carriers by a QW,
as well as to obtain analytical expressions for the determining the time of capture of free charge carriers, the time of
carrier emission from the QW, and the establishment of a correlation between them.
Tomsk State University of Control Systems and Radioelectronics, Tomsk, Russia, e-mail: email@example.com.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 19–25, February, 2018. Original article
submitted May 30, 2017.
1064-8887/18/6102-0223 2018 Springer Science+Business Media, LLC