Self-Induced Photon Absorption by Screening of the Electric Fields in Nitride-based Quantum Wells
- PDF / 69,984 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 104 Downloads / 175 Views
L11.5.1
Self-Induced Photon Absorption by Screening of the Electric Fields in Nitride-based Quantum Wells S. Kalliakos, P. Lefebvre, T. Taliercio and B. Gil GES – CNRS – Université Montpellier II. CC 074, 34095 Montpellier Cedex 5, France. ABSTRACT We have calculated the change of interband absorption spectra of a quantum well based on hexagonal group-III nitride semiconductors under photo-injection of high densities of electron-hole pairs. The screening of internal electric fields by such optical excitation is known to blue-shift and reinforce the ground-state optical transition. Due to the large values of densities of states and of internal fields, we predict novel properties that rather concern optical absorption via transitions between excited states. The absorption coefficient can be strongly enhanced by the optical excitation itself, in this particular spectral region, yielding the possibility for self-induced absorption properties. In other words, if sufficiently intense, an excitation laser can increase the absorption coefficient of the system at its own wavelength, thus providing a strong nonlinear optical response. Finally, we briefly discuss the potential application of these optical phenomena.
INTRODUCTION After the first demonstration of a light emitting device based on hexagonal (wurtzite) group-III nitride semiconductors [1], the interest of the scientific community has risen up considerably. Low-dimensional structures, like quantum wells (QWs) or quantum boxes (QBs) have received the main part of the attention since it was clear that the understanding of the physical processes that are responsible for the light emission mechanisms in these structures would lead to an improvement of the device performance. The main peculiarity of these quantum systems is the presence of huge internal electric fields, in the order of 1 MV/cm, along the growth axis, due to the difference of both spontaneous and piezoelectric polarization between the barrier and well materials [2-4]. Because of this electric field, the optical transitions exhibit a large red-shift, even below the material band-gap, due to the quantum confined Stark effect (QCSE) [5-10]. Also, the electrons and holes are separated at the opposite sides of the well (box) [5,8,11,12] leading to a considerable increase of the radiative recombination time. Lifetime changes by several orders of magnitude can be obtained simply by increasing the well (box) width (height) by few nanometers [8]. In this work, we investigate the behavior of a GaN-based quantum well under high photoexcitation conditions. In particular, we calculate the entire absorption spectrum of such a system, including the excited states, and we follow its evolution when a high density of electron-hole pairs is injected. Until now, a number of interesting phenomena have already been predicted and/or experimentally verified like, for example, the bleaching of the excitonic interaction [13]. We are mainly interested in the screening of the electric field [14-16] which can lead, among others, to
Data Loading...
