Optimization of laser heterostructures for mid- infrared
Leonid V. Danilov1, Georgy G. Zegrya1
1 Ioffe Physical-Technical Institute, St. Petersburg 194021, Russia e-mail: danleon84@mail.ioffe.ru
Abstract—Theoretical analysis of radiative and non-radiative recombination in deep QWs was done and the design of new mid- IR lasers with high quantum efficiency was proposed.
I. INTRODUCTION
Two main carrier-recombination mechanisms exist in semiconductors at high excitation levels: radiative recombination (with emission of a photon), and nonradiative Auger recombination (AR) involving an electron-electron or hole-hole interaction. In this context, the two most likely AR processes are distinguished: CHCC-process involving two electron and a heavy hole, and CHHS-process involving an electron and two heavy holes, with a transition of one of these holes into the spin-orbit split-off band. In homogeneous semiconductors, processes of this kind are of threshold nature [1]. Limitations on the AR rate are imposed by the energy and momentum conservation laws for carriers. However, the limitations imposed by the quasi-momentum conservation law are lifted in heterostructures (quantum wells, wires, and dots).
As a consequence, additional, more efficient, zero-threshold Auger recombination channels appear in systems of this kind.
This is particularly clearly pronounced in narrow-gap semiconductors, which hinders development of an IR semiconductor heterolaser with efficient operation at room temperature.
II. THEORETICAL ANALYSIS
In [2], it was suggested that heterostructures with deep and narrow QWs for electrons and holes can be used in order to obtain an IR laser. In structures of this kind, the zero-threshold AR mechanisms can be strongly suppressed. For this purpose, it is necessary that the following conditions should be satisfied:
(U Uc, v)>Eg and E2-E1 >Eg (where E1 and E2 are the energies of the first and second quantum-well levels of electrons, Uc and Uv are the depths of QWs for electrons and holes, respectively, and Eg is the energy gap). In QWs of this kind, the excitation energy is insufficient for release of an electron into the continuous spectrum (zero-threshold mechanism) or its transition to the second quantum-well level (resonant mechanism). Modern technologies enable fabrication of structures of this kind on the basis of InAs(Sb)/Al(As)Sb and InAs/GaSb/AlSb materials.
It is shown how the total AR coefficient (order-of- magnitude values) depends on the QW width for Al(As)Sb/InAsSb/Al(As)Sb heterostructure. For a given composition of heterostructure, the region of AR suppression corresponds to the width of the quantum well 9-11nm, when the only AR mechanism is the threshold of the CHCC-process.
The plot suggests that the threshold process is the slowest in our system, and the AR coefficient for this process is two-three orders of magnitude smaller than those for the other two considered processes. Thus, it is apparent that a correct choice of the parameters of the heterostructure ( ,a U Uc, v) does enable considerable suppression of the nonradiative AR via elimination of its fastest processes.
Earlier in [3] has been demonstrated that laser heterostructure can also be optimized on the number of quantum wells. In the work [4], the dependence of the threshold drive-current density on the number of QWs in Al(As)Sb/InAsSb/Al(As)Sb heterostructure was presented. In this case, the width of the quantum well belongs to the region of AR suppression, a=10nm. The obtained plot shows that for a short cavity the dependence exhibits a pronounced minimum at
QW 3
N = . At the same time, the internal quantum efficiencies have close values about 80 percent. As the number of QWs in the SL increases, tends to a constant value of about 85 percent.
It is important to note that this result was obtained for T=300K.
ACKNOWLEDGMENT
This work was in part supported by grant RFBR RAS №14- 02-31409.
REFERENCES
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Akad. Nauk, St. Petersburg, 1997).
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“Threshold characteristics of InGaAsP/InP multiple quantum well lasers”, Semicond Sci. Technol., 2000, v.15, pp. 1131-1140.
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