H. Haug

Optical properties of highly excited direct gap semiconductors

Abstract The electronic excitations in direct gap semiconductors interact strongly with the photon field. We discuss both the experimental and the theoretical aspects of the optical properties of these materials under strong optical excitation. We distinguish between intermediate excitation levels at which the electronic excitations form a dense system of excitons and excitonic molecules and very high excitation levels at which a degenerate electron-hole plasma occurs. The optical spectra of dense excitonic systems, which are mainly observed in copper halides and II–VI compounds, are shown to be determined mainly by the interaction processes between excitonic molecules, polaritons and free carriers. The optical properties of the electron-hole plasma, which has been observed in II–VI and especially in III–V compounds, can be understood only by taking into account many-body effects, such as dynamical screening of the Coulomb interactions, plasmon-assisted transitions and excitonic enhancement.

Optical Nonlinearities and Instabilities in Semiconductors

The main mechanisms for the observed large optical nonlinearities in semiconductors are briefly discussed and illustrated for the example of the exciton ionization by plasma screening. These nonlinearities cause various types of optical bistability, either of intrinsic nature or evoked by an additional resonator feedback. Under certain operation conditions also higher instabilities such as oscillations and chaos can be obtained. As an example, the self-pulsing of an induced absorber in a ring cavity is treated. The resulting locked oscillations are shown to follow a Farey-tree scenarium.

Condensation effects of excitons

Abstract The theory of the electronic excitations in a highly excited semiconductor is presented. The relaxation processes, the formation of excitons and excitonic molecules, the interaction among the various forms of electronic excitations, as well as their optical and thermodynamical properties are analyzed. At low temperatures one expects condensations into the quantum statistically degenerate phases of the excitonic molecules and of the electron-hole plasma. The physical properties of these low temperature phases are investigated. Possibilities and previous attempts to observe the Bose-Einstein condensation in excitonic systems are discussed critically. The experimental observations of the electron-hole liquid phase transition are reviewed.

Theory of noise in semiconductor laser emission

For the complex light field amplitude of a semiconductor laser an equation of a generalized van der Pol oscillator with a fluctuating driving term is derived from first principles. This equation is shown to be valid for optical band-to-band transitions with and withoutk-selection rule. Neglecting the nonlinearity in the saturation higher than of second order and also the intensity dependence of the dispersion this equation reduces to the standard van der Pol equation with a noisy driving term. From the general equation the linewidth and the noise of the intensity of the laser emission is calculated above and below threshold. The results are in agreement with the experimental data ofArmstrong andSmith.

Optical switching in low-dimensional systems

The workshop was a part of the NATO Special Program on Condensed Systems of Low Dimensionality (1983-1988). Contributors concentrate on the development and study of optical and electro-optical devices, as well as experimental and theoretical investigations of the underlying optical nonlinearities. T

BOSE-EINSTEIN STATISTICS IN THERMALIZATION AND PHOTOLUMINESCENCE OF QUANTUM-WELL EXCITONS

Quasi-equilibrium relaxational thermodynamics is developed to understand LA-phonon-assisted thermalization of Bose-Einstein distributed excitons in quantum wells. We study the quantum-statistical effects in the relaxational dynamics of the effective temperature of excitons

Subband-level renormalization and absorptive optical bistability in semiconductor multiple quantum well structures☆

T = T(t)

Nonequilibrium properties of electron-hole plasma in direct-gap semiconductors

. When

Simplified calculations of the optical spectra of two- and three-dimensional laser-excited semiconductors

T

Optics of excitonic molecules in semiconductors and semiconductor microstructures

is less than the degeneracy temperature