GENERATION OF FAST-SWITCHING AS2 AND P2 BEAMS FROM ASH3 AND PH3 FOR GAS-SOURCE MOLECULAR-BEAM EPITAXIAL-GROWTH OF INGAAS/INP MULTIPLE-QUANTUM-WELL AND SUPERLATTICE STRUCTURES

In an attempt to maximize the cracking and dimerization efficiencies with the use of Ta baffling, a severe memory effect was observed which necessitated excessive growth pause durations for group V beam switching. This memory effect was significantly reduced by the implementation of separate Ta-tube catalytic hydride crackers for each group V source. A comparison of W and Ta tubes revealed that the catalytic effect which was observed for the decomposition of AsH3 and PH3 on a Ta surface was not observed for a W surface. The improved high-conductance design yielded cracking and dimerization efficiencies on the order of 99% and 90%, respectively. Switching characteristics have been studied using time-resolved quadrupole mass spectrometry, and switching times of < 1 s have been achieved for As2 and P2 with significantly longer switching times observed for As4. Multiple layer heterostructures have been grown with the baffled/common cracker and the separate open-tube crackers for evaluation of the memory effects by secondary ion mass spectrometry. InGaAs/InP quantum well structures have been grown with the fast-switching crackers. Double crystal x-ray diffraction, transmission electron microscopy, and low temperature photoluminescence (PL) characterization suggest that the interfaces obtained with the fast-switching crackers are abrupt to within approximately 5 angstrom when short growth interuptions (approximately 10 s) are used. However, low temperature (5 K) PL excitation spectra indicate that an interface asymmetry is present. These data suggest that despite verification of fast AS2 and P2 switching using time-resolved quadrupole mass spectrometry, growth pause optimization, and group III flux stabilization are still required in order to obtain optimal interface quality for InGaAs/InP heterostructures.