The effects of step bunching on a CuPt-B ordered structure in Ga0.5In0.5P grown on (11n) B and (11n) A (n=8, 13) GaAs substrates by metalorganic vapor phase epitaxy (MOVPE) are described. In the GaInP layers, a CuPt-B ordered structure in the  B and  B directions are formed. The epitaxial growth surfaces are often undulated due to the atomic-step bunching. Experimental results for a low V/III ratio of 55 shows that a disordered region of the CuPt-B or-dered structure is formed at the step-bunched surface. Also, anti-phase domain boundaries of the CuPt-B ordered structure are formed on terraced surfaces for V/III ratio of 1500. The ordered structure domain formation is thought to depend on the growth on surface facets which are formed through P-dimer distribution there.
Kelvin probe force microscopy (KFM) was successfully applied to the two-dimensional potential profile measurements of the cleaved surface of GaAs HEMTs under bias voltage. A high-field region was observed at the drain-side edge of the gate. By measuring the cleaved surfaces of GaAs/AIAs and InAlAs/InGaAs heterostructures, we have obtained potential profile reflecting the work function difference of the material. The minimum distinguishable thickness of the InAlAs/InGaAs heterostructure by the KFM was 40nm. The present KFM technique combined with device simulation will provide a powerful tool for analyzing the electrical properties of the device, not only GaAs devices but also others.
An evaluation method for mutilayered semi-conductors by Auger depth profiling analysis is described. We have determined the depth resolution function (DRF) from the Auger depth profile of GaAs/A1GaAs specimen having an abrupt interface. Then, we have applied the DRF to the analysis of an interface of GaAs/AlGaAs specimen containing an interface of aluminum graded-layer. The resulting aluminum graded-layer thickness is about 14nm, which is in good agreement with the value estimated from the growth rate of the thin layer at preparing the specimen with molcular beam epitaxy method. The general formula of the depth resolution function was obtained from the logistic function. We have also carried out the evaluation of InP/GaInAs mutilayer structures by Auger depth profiling analysis. It is very difficult to obtain the Auger depth profile of InP specimens by argon ion sputtering because of the induced surface roughness. To reduce the roughness caused by the argon ion bombardment, a specimen cooling method (at liquid nitrogen temperature) was applied to the Auger depth profiling analysis of InP (8nm)/GaInAs (6nm) mutilayered specimen. This method provided excellent results ; the mutilayered structure of the multi-quantum wells was observed clearly over the 40 structures (over the depth of 300nm).
By in-situ surface photo-absorption (SPA) monitoring of MOVPE grown GaAs(111)B surface, three types of surface phases, (2×2)-like, (√19×√19)-like, and (1×1)HT-like, are identified. Eight-μm-wide atomically step-free surfaces and interfaces are successfully obtained by controlling the surface phase and by using finite area epitaxial (FAE) growth. Their flatness is confirmed by ex-situ AFM and low-temperature (4K) spatially resolved photoluminescence (SR-PL) measurement. A flattening principle of FAE is discussed, where two-dimensional (2D) nucleation is suppressed on GaAs(111)B surface due to desorption and surface migration. It is concluded that, by utilizing desorption, a step-free surface of any size can be formed as long as the size is finite. To demonstrate this, an extraordinarily wide step-free GaAs(111)B surfaces 100μm in diameter are successfully formed. Surface stoichiometry control based on insitu SPA monitoring is indispensable for flatness control.
Two-dimensional dopant profiles of LSI device cross-sections are extracted below 100nm scale from SCM (Scanning Capacitance Microscopy) technique. Sample cross-sections are prepared with a glass polishing technique, followed by a final polishing step with a colloidal silica. Samples are also fabricated with FIB (Focused Ion Beam) to acquire SCM images on specific cross-sections of devices, which become effective for failure analysis. The phosphorus profiles of P-doped Si substrate and DRAM device are imaged within the range of 1×1016-2×1019 atoms/cm3 with the lateral resolution of 50-60nm. The chemical bonding states of glass-polished and ion-milled Si-surfaces are also examined by XPS (X-ray Photoelectron Spectroscopy). The influence of the surface bonding-states on SCM images is discussed.
In order to investigate the formation process of self-assembled monolayers (SAM) of alkanethiol, we analyzed the molecular organization by Fourier-transform infrared reflection-absorption spectroscopy (FT-IR-RAS). The spectra suggested that molecular structure of the SAM on gold (111) surface is dependent on the immersion time. Alkanethiol in the SAM aligns normal to the substrat surface. A stable SAM embedded a close packed monolayer by the van der Waals interaction among alkanethiol and surface force from the gold substrate.
Low energy electron microscopy (LEEM) is a powerful tool for the study of surface structure, and incorporation of an imaging energy filter in a LEEM instrument offers numerous new possibilities that increase the amount of information. We have developed an energy-filtering LEEM instrument, where a Wien filter was adopted for energy selection. One of the advantages of the Wien filter is its straight optic axis, which is exceptional among energy filters. Owing to this nature, tuning of optical conditions for energy-filtering imaging is greatly simplified. However, no successful result for the production of an imaging Wien filter had been reported; this fact may be due to the lack of consideration to aberrations in the process of practical design. This article describes the electron optical work we have done for the realization of an imaging Wien filter.