Material Engineering of Novel Semiconductor Structures.
Final rept. 1 Jun 1989-30 Nov 1990
JOHNS HOPKINS UNIV BALTIMORE MD DEPT OF ELECTRICAL AND COMPUTER ENGINEERING
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The first experiments were done in the visible region of the spectrum, using familiar nonlinear material ZnSe in order to acquire experience in nonlinear spectroscopy. Highly sensitive measurements of the spectrum of nonlinear refractive index of ZnSe were done using the method of self-bending. This method, has shown significant advantage over conventional Kramers-Kronig method. The results of the measurements were somewhat unexpected, since the nonlinear index of refraction, n2 measured by us turned out to be quite large 10 to the -8th power sq. cm.W and hard to explain using conventional wisdom of the thermally-induced bandgap shrinking. Therefore, we conducted additional set of measurements that gave the proof of the excitonic origin of the nonlinearity. After the near-infrared laser became fully operational, the main thrust was in the direction of investigation of nonlinear optical and electro- optical properties of the asymmetric coupled QWs. Efforts to locate reliable sources of MBE-grown QW material had finally succeeded. First experiments on photoluminescence and photoconductivity spectroscopy of asymmetric coupled QWs started. The samples used had 25 coupled QW periods each consisting of two Al0. 357 Ga 0.65 As QWs, with thickness of 18A and 32A separated by 15A GaAs barrier. Thicker 100 A barriers separated the coupled QWs from each other. The entire undoped multiple QW structure was sandwiched between n and p Al0.35 Ga 0.65 As layers.
- Lasers and Masers
- Electrooptical and Optoelectronic Devices