Surfactant-Mediated Growth of SiGe/Si Quantum-Well Structures Studied by Photoluminescence Technique and Secondary Ion M
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ABSTRACT In this investigation, surfactant-mediated growth of SiGe/Si single quantum-well structures is studied by photoluminescence and secondary ion mass spectrometry. The samples were grown by molecular-beam epitaxy and Sb was used as a surfactant. The photon energy of the SiGerelated near-band-edge photoluminescence was used to probe the action of Sb as a surfactant to promote two-dimensional growth and to reduce segregation of Ge during growth. First, the "growth-temperature window" at which Sb acts preferentially as a surfactant was determined. Then, at this optimized temperature of 700'C, the influence of different Sb coverages was investigated and it was found that 0.5 monolayer was a sufficient coverage to obtain full surfactant action. Ge concentration depth profiles obtained by secondary ion mass spectrometry confirmed the effect of surfactant-mediated growth and, in addition, the unintentional incorporation of the Sb surfactant during growth was determined quantitatively. In a final experiment the effect of deposition of Sb on either the lower or the upper heterointerface is addressed. INTRODUCTION Structural and chemical interface imperfections in the form of morphological roughness and compositional fluctuations are limiting factors of the performance of devices based on semiconductor heterostructures [L]. With different epitaxial techniques and a high level of options for control of the growth and characterization, it has now become possible to deposit ultrathin layers with well-defined thicknesses of only a few monolayers (MLs) and with abrupt heterointerfaces to within IML [2]. Generally, to obtain these high quality heterointerfaces, the growth mechanism is attributed to two-dimensional modes of growth. In the case of heteroepitaxy of lattice-mismatched materials like the SiGe/Si heterostructure system, the requirement on the growth process is even more crucial since the induced strain may lead to a breakdown of the epitaxy coherence. In this context the question may arise how to suppress three-dimensional island formation during growth. Recently, the use of an additional surface species during growth, a surfactant, has been shown to be succesful in order to hamper island formation and to reduce segregation of the constituents of the growing layer [3]. The present work focusses on surfactant-mediated molecular-beam epitaxial (MBE)-grown SiGe single quantum wells. Since the heterointerface quality as well as the compositional variation in the quantum well strongly influence the optical properties, the photon energy of the near-band-edge photoluminescence (PL) was used to investigate surfactant-mediated growth using Sb as a surfactant. In addition, measurements of the heterointerface quality and the unintentionally incorporated Sb concentration were given by secondary ion mass spectrometry (SIMS)-depth profiles.
197 Mat. Res. Soc. Symp. Proc. Vol. 399 01996 Materials Research Society
EXPERIMENT The samples were grown pseudomorphically in a commercial solid source MBE system (V80S) equipped with t
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