Y. J. Ding

Characterization of recombination processes in multiple narrow asymmetric coupled quantum wells based on the dependence of photoluminescence on laser intensity

Continuous‐wave intensity‐dependent photoluminescence spectra of multiple narrow asymmetric coupled quantum wells at room temperature have been measured. At low laser intensity, the total photoluminescence intensity is primarily proportional to the square of the laser intensity due to dominant nonradiative recombination of free carriers at nearly saturated interface traps. At high laser intensity, however, the total photoluminescence intensity approaches a level proportional to the laser intensity due to radiative recombination of free carriers. Based on this transition behavior, which has been observed for the first time to the best of our knowledge, and our simple theory, the transition intensity, the nonradiative decay time of the carriers, and the intensity‐dependent carrier density and photoluminescence quantum efficiency have been determined.

Continuous‐wave photoluminescence excitation spectra of multiple narrow‐stepped quantum wells: Evidence for saturation of interface traps

Continuous‐wave photoluminescence excitation spectra of multiple narrow‐stepped quantum wells at room temperature have been measured for the first time. It has been observed that photoluminescence intensity increases stronger than proportionally to the square of the laser intensity. This phenomenon can be attributed to the radiative recombination between free carriers in parallel with the dominant nonradiative recombination on the saturable interface traps. Intensity‐dependent trapping efficiency and ratio between electron and hole nonradiative decay times, and the ratio between trapping and nonradiative recombination rates have been derived from the experiment.

Spectral measurement of the nonlinear refractive index in ZnSe using self-bending of a pulsed laser beam

The nonlinear refractive-index (n(2)) spectrum of ZnSe near the band gap (lambda(gap) approximately 450 nm) at 77 K was measured for the first time to our knowledge by using self-bending of a pulsed laser beam. The maximum nonlinearity, n(2) approximately 1.9 x 10(-8) cm(2)/W, measured by us is anomalously large, which cannot be explained by conventional thermally induced band-gap shrinkage.

Observation of anomalously large blue shift of the heavy‐hole photocurrent peak and optical bistability in narrow asymmetric coupled quantum wells

Blue shift of the heavy‐hole peak of the photocurrent spectra has been observed, for the first time, in narrow GaAs/Al0.4Ga0.6As asymmetric coupled quantum wells near the heavy‐hole resonance. With an external reverse bias of only −2.35 V, a maximum upward shift of the apparent peak position of ∼6.1 meV has been measured at 78 K. Sharp change of the inhomogeneous linewidth of the heavy‐hole peak has also been observed. cw optical bistability has been observed with the external feedback.

Demonstration of strong saturation of traps in multiple, narrow, slightly asymmetric coupled quantum wells

Continuous-wave photoluminescence excitation spectra of multiple, narrow, slightly asymmetric coupled quantum wells at room temperature have been measured. As the laser intensity increases, the photoluminescence intensity initially increases at a rate that is higher than square-law dependence and finally approaches square-law dependence. This phenomenon can be attributed to the process in which a dominant nonradiative recombination at the traps undergoes strong saturation with weak radiative recombination of free carriers. The intensity-dependent trapping efficiency and ratio between electron and hole nonradiative decay times, and the ratio between trapping and nonradiative recombination rates have been determined from the experiment.

Strong excitonic nonlinearity in a P-I-N photodiode incorporating narrow asymmetric coupled quantum wells

Strong excitonic nonlinearity in the photoconductive response of a P-I-N photodiode incorporating narrow asymmetric coupled quantum wells has been observed at 78 K. When the P-I-N photodiode is overbiased, the heavyhole energy levels in the two coupled quantum wells are moved toward the resonance by increasing the laser intensity. Also, both the light-hole and the heavy-hole excitonic transitions undergo intensity-dependent shifts. Both these effects indicate intrinsic change of bias due to redistribution of photogenerated carriers and, therefore, the existence of an intrinsic feedback mechanism. The magnitude of the blue shift of the heavy-hole excitonic transitions significantly increases when the laser intensity is changed from 9.2 to ~270 mW/cm(2).

Dynamics and stability of hysteretic and multiphoton optical resonances of a single slightly relativistic cyclotron electron

The stability of hysteretic cyclotron resonance, subharmonic optical excitation, and biharmonic optical cyclo-Raman resonances of a single electron is analyzed. A simple criterion of small-perturbation stability is derived whereby for the main resonance and subharmonic resonances those states are stable for which the derivative of the electron energy with respect to driving intensity is positive and vice versa. For the cyclo-Raman resonances in the absence of isolated states (the so-called isolas) the stability criterion is the same, whereas in the presence of the isolas it is reversed above the point of self-crossing in each isola. We also explored the behavior of the system in-large, using phase portraits and demonstrated existence of corridors of attraction as well as phase multistability in subharmonics and higher-order cyclo-Raman excitation.