Bistable Semiconductor Research Articles

Time dependent analysis of active and passive optical bistability in semiconductors

A time-dependent theory of optical bistability is developed and applied to laser amplifiers and passive semiconductor etalons. Results of the theory show an output intensity spike in switch-up which occurs after a time delay determined largely by the carrier recombination time, and before which the transition is unstable. Although for passive etalons the spike is rather broad (of order 1 ns for parameters appropriate to GaAs at 0.85 μm or InGaAsP at 1.55 μm) and of low amplitude, for amplifiers it is roughly an order of magnitude narrower and higher in amplitude. As a consequence, it is predicted that clock speeds for semiconductor bistable switching elements will be limited to rates commensurate with the carrier recombination time, not only for switch-down operations (as already well known) but also for switch-up operations.

Theoretical explanation of the absorptive optical bistability in semiconductors due to band-gap shrinkage

The creation of an electron-hole plasma in a semiconductor leads to a large band-gap shrinkage which can be used to obtain absorptive optical bistability caused by discontinuous jumps between states of weak band-tail absorption and states of strong band-edge absorption. These effects are described by rate equations for the photons and the free carriers. For CdS the calculated hysteresis phenomena are similar to the experimental results.

Many-Body Theory of Optical Bistability in Semiconductors

Many-Body Theory of Optical Bistability in Semiconductors

Optical input and output characteristics for bistable semiconductor lasers

Experimental results are presented regarding the switching of a bistable semiconductor laser’s output (PO) with injected optical power (PI). An incident optical beam, generated by an ordinary semiconductor laser, was injected into the bistable semiconductor laser with inhomogeneous excitation. The mutual relation between PI-PO characteristics and I-L characteristics for the bistable laser, and the dependence of PI-PO characteristics on the bias current of the bistable laser are described. Switching between the two stable bistable operation states is accomplished by injecting optical trigger pulses. Switching of the laser having differential gain characteristics, through use of optical pulse, is also looked at.

Optical nonlinearity and bistability in semiconductors due to biexciton formation

The exciton polariton spectrum shows intensity- dependent anomalies due to the virtual formation of biexcitons. This renormalization is treated by calculating the intensity-dependent polarization function which in turn determines the dielectric function. The results of the two-photon Raman scattering experiments are fitted for CuCl and CdS. This nonlinearity is shown to be well-suited to produce a mainly dispersive optical bistability.

Optical bistability in semiconductors

Detailed results are presented on optical bistability (OB) and two-beam optical transistor (transphasor) action in simple, one-element Fabry-Perot devices, with the semiconductor InSb using a CW CO laser near the bandgap region, and OB for semiconductors in general is discussed. OB and multistability are seen in transmission and reflection at 5 K. At 77 K, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n_{2} \simeq 3 \times 10^{-3}</tex> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /W [corresponding to an effective <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\chi^{(3)} \sim 1</tex> ESU] is measured and OB is observed at ∼8 mW. Transphasor action at 5 K is presented and the influence of degenerate four-wave mixing is discussed. The basic physics of the microscopic mechanism for n <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (bandgap-resonant saturation) is summarized and a simplified, generalized model is derived. This model and arguments on cavity optimization are used to predict order of magnitude limits to switching power, energy, and speed, both in InSb and other semiconductors, even in the absence of excitonic enhancement.

Optical bistability in semiconductors

Optical bistability has been observed in a semiconductor for the first time. The bistable etalon consists of a GaAlAs-GaAs-GaAlAs molecular-beam-epitaxially-grown sandwich with 90% reflectivity coatings. The bistability is primarily dispersive with the nonlinear refractive index arising from light-induced changes in exciton absorption. Using light of frequency just below the exciton peak, we observed bistability from 5 to 120 °K with 40-ns turn-off and subnanosecond turn-on times with 1 mW/μm2 holding intensity.