坂東 弘之

A new method of InP substrate cleaning is presented for molecular beam epitaxy (MBE). It is based on the congruent sublimation of InP at a temperature of 380 ± 50 ° C and is phosphorous-beam free, so that the substrate cleaning can be carried out in the preparation chamber with no phosphorous K-cell provided. This is important to keep the growth chamber free from degassing during substrate preparation. InGaAs-InAlAs MQW epilayers grown on InP substrates cleaned by the present method were characterized crystallographically, optically and electronically, demonstrating that the quality is as good as that of those grown on a substrate cleaned by the conventional method. © 2005 Elsevier B.V. All rights reserved.

Misfit dislocation was investigated by observing crosshatch over surfaces of InxGa1-xAs-In0.52Al0.48As strained multiple quantum wells (MQWs) and InxGa1-xAs bulk-like thin epifilms grown on InP substrates. It was found that no crosshatch was observed on surfaces of non-doped InxGa1-xAs-In0.52Al0.48As strained MQW over an In composition range of 0.32 < x < 0.78 and that Be-doped InxGa1-xAs bulk-like thin films were also crosshatch free over a wide range of 0.42 < x ≤ 1.0, which clearly exceeds the critical thickness limit. Surface and cross-sectional diagnostics and a preliminary result on the electron mobility of the crosshatch-free InAs bulk-like thin films were presented. © 2005 Elsevier B.V. All rights reserved.

Optical absorption saturation density I-s was measured for InxGa1-xAs-In0.52Al0.48As multiple quantum well structures grown on InP (100) substrates by molecular beam epitaxy. Indium composition x was varied from 0.32 to 0.70 so that the quantum well layer was under tensile strain (x < 0.53), lattice matched (x = 0.53), or compressive strain (x > 0.53). Optical measurement was carried out using femtosecond light pulses from the optical parametric amplifier of a mode-locked Ti-sapphire laser amplifier. The density I-s in a sample changed as a function of photon energy and exhibited a minimum value at the band-edge exciton energy. This minimum, showed the smallest value at x = 0.46 (under tensile strain) of all the samples with different x. This was in marked contrast to the results reported in the literature. Degenerate pump-probe measurement was also carried out, and the results showed that the relative transmission change Delta T/T measured at zero delay between the pump and probe pulses exhibited the largest value at x = 0.46, confirming the result of I-s measurement.

Optical absorption saturation intensity Is was measured by using femtosecond light pulse for InxGa1-xAs-In(0.52)Al(0.48)AS MQW grown on InP (100) substrates. Is showed minimum at x=0.46 (under tensile strain). This was in marked contrast to the previous results.