Inhibited and Enhanced Spontaneous Emission from Optically Thin AlGaAs/GaAs Double Heterostructures

Abstract

Inhibited spontaneous emission in atomic physics has been intensively investigated recently. In solidstate physics these effects are no less important. We have studied the spontaneous emission of light from electron-hole recombination in optically thin GaAs double heterostructures. The electron-hole radiative recombination rate coefficient B is not purely a property of the GaAs itself, but depends strongly on the optical-mode density and refractive index of the medium in which it is immersed. The spontaneousemission rate can be markedly increased or decreased depending on whether the surrounding refractive index is higher or lower than that of GaAs. 32.70.Fw, 78.55.Cr, 78.65.Fa Inhibited spontaneous emission in atomic physics has been intensively investigated recently. 1-3 In solid-state physics these effects are no less important. The concept of a "photonic band structure" has been proposed 4,5 in which a three-dimensional periodic face-centered-cubic dielectric structure has a forbidden gap for photon modes. The influence of one-dimensional periodic layering 6 has also been investigated. In this paper, we will show that simply changing the index of refraction of the surrounding medium can already have a pronounced effect on spontaneous-emission rates.Double heterostructures of the III-V semiconductors are among the handful of condensed-phase systems 7,8 capable of radiative quantum efficiency approaching unity. In addition, spontaneous emission plays an important role in many types of electronic devices, such as semiconductor lasers. Such solid-state systems can be readily immersed in optical media of widely varying index of refraction. The spontaneous-emission rate will depend on the refractive index Az e xt of the host medium, which may be greater or less than the n inX of the radiating substance itself.The rate of spontaneous emission is usually given by Fermi's "golden rule": -±-=^\(\xEL\>\ 2 p(co),where TR is the radiative lifetime which we seek to influence, x is the material dipole operator, E\ ni is the electric field creation operator inside the luminescent material, and pica) is the total density of optical modes per unit energy at the angular frequency co. Attention is generally directed toward the density of states, which in an external optical medium is nj xi times greater than in vacuum:(2) x 2 hc 3 where V is the normalization volume of the optical modes. Most of the interesting physical questions will be connected with the electric field creation operator E^t inside the excited luminescent material. This operator creates a single photon; thus the electric field magnitude associated with this operator can be regarded as the "field of a single photon" which is in turn related to the "zero-point electric field." Therefore an investigation of spontaneous-emission properties in condensed matter structures is also an investigation of the local distribution of zero-point electric field fluctuations. (In empty space these would have been called vacuum fluctuations.)We will show that a determination ...

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