Atomic and Electronic Structure of III-V Semiconductor Surfaces

Doktorsavhandling, 1996

The atomic and electronic structure of clean and Cs-perturbed III-V semiconductors was studied by angle-resolved photoelectron spectroscopy (ARPES), surface core level spectroscopy (SCLS), and scanning tunneling microscopy (STM). The work can be divided into three parts, dealing with low-index sur-faces, high-index surfaces, and special features of InAs. The low-index investigations include the (1,-1,-1,- )3x3, (100)4x1, (1,-1,-1,-)2x2, and (111)2x2 surfaces of InSb and the (1,-1,-1,- )2x2 and (111)2x2 surfaces of InAs. For both materials the (1,-1,-1,- )2x2 were prepared by molecular beam epitaxy (MBE), while the other surfaces were obtained by ion bombardment and an-nealing (IBA). Results from ARPES, SCLS, and STM are presented that cast doubt on the current structural model of InSb(1,-1,-1,-)3x3. The (111)2x2 and (1,-1,-1,- )2x2 surfaces were studied by ARPES and SCLS. Great similarities were ob-served in the elec-tronic structures of the two materials. The results support previous structural models of both 2x2 InSb faces, and show that the same models also apply to the corresponding InAs surfaces. All surfaces were found to be semicon-ducting, in accord with general experience of compound semiconductors. Structural studies of high-index surfaces were made on GaAs(311)A and InSb(211), prepared by IBA. In both cases the surfaces were observed to have 1x1 periodicity. The GaAs sur-face was studied by ARPES and SCLS. From the data conclusions were drawn about atomic structure. Both (211) surfaces were studied with ARPES, SCLS, and STM. The B-face was found to be atomically flat and well ordered, while the quality of the A-side was less perfect. These three high-index surfaces were also found to be semiconducting. Special attention was paid to electron accumulation on InAs surfaces. By using ARPES the presence of an electron gas could be directly observed. The phe-nomenon was shown to be a common property of clean IBA and MBE prepared InAs surfaces and was ascribed to donor-type defects. Another anomalous behaviour of InAs was revealed after sub-monolayer deposition of Cs; emission from a bulk interband transition was shown to be very sensitive to this surface perturbation, even more so than emission from surface states.