Jun-ya Ishizaki

Mechanism of Multiatomic Step Formation during Metalorganic Chemical Vapor deposition Growth of GaAs on (001) Vicinal Surface Studied by Atomic Force Microscopy

The detailed behavior and mechanism of multiatomic step formation processes during metalorganic chemical vapor deposition (MOCVD) of GaAs on vicinal surfaces are systematically investigated using an atomic force microscope (AFM). Under the low growth rate condition, the step flow growth mode with regular stripe is obtained, and the final terrace width is almost independent of the substrate misorientation angle. The result suggests that the barrier height difference for surface migrating Ga atoms between the terrace site and the step site is small, and the final terrace width is mainly determined by a migration length. Three-dimensional nucleation and growth mode with irregular steps are also obtained under the high growth rate condition. However, as the AsH3 partial pressure increases, irregular steps are no longer observed. For these results, we discuss the multiatomic step formation mechanism.

Formation and photoluminescence characterization of quantum well wires using multiatomic steps grown by metalorganic vapor phase epitaxy

Abstract GaAs/AlGaAs quantum well wires (QWWs) were successfully fabricated using multiatomic steps on GaAs vicinal substrates by metalorganic vapor phase epitaxy (MOVPE). Coherent multiatomic steps with extremely straight step edges were observed on GaAs and AlGaAs epitaxially grown layers on vicinal substrates over a wide observation area by atomic force microscopy (AFM). Formation of QWW structures is due to the fact that the GaAs growth rate on AlGaAs with multiatomic steps is much larger at the corners of steps than on the terraces. GaAs QWWs at the corners of steps accompanied by quantum wells (QWs) on the terraces were observed in cross-sectional transmission electron microscope (TEM) images. Photoluminescence (PL) of QWWs was measured at 20 K. The PL peak energy of the QWW structures grown on 5.0°-misoriented substrates was 23 me V smaller than that of a reference QW structure on an exactly oriented substrate. Since the total amount of the grown material is basically the same for both structures, this peak energy shift indicates the formation of quantum-wire-like structures at the corners of multiatomic steps. Furthermore, this observed red shift is in good agreement with a simple theoretical estimate of the QWW structures observed by TEM. These results suggest that the present novel fabrication method of QWWs is very promising for the formation of uniform nano-meter size quantum wires without any processing damage.

Multiatomic step formation mechanism of metalorganic vapor phase epitaxial grown GaAs vicinal surfaces and its application to quantum well wires

The multiatomic steps formed on GaAs vicinal surfaces by metalorganic vapor phase epitaxy (MOVPE) are studied by atomic force microscopy (AFM). An AFM image of an epitaxially grown GaAs surface showed coherent multiatomic steps with extremely straight edges over a wide area. The average height and spacing of the multiatomic steps are 1.2-8 and 30-110 nm, respectively. These terrace widths change with the growth conditions. Narrower terrace widths are obtained at higher growth rates, and under higher AsH 3 partial pressures and higher impurity doping conditions. The results suggest that the migration distance of a Ga atom on the terrace and the sticking coefficient at the step sites depend on these growth conditions. Using multiatomic steps, GaAs/AlGaAs quantum well wires (QWWs) were grown on a GaAs vicinal surface. Cross-sectional transmission electron microscopy and photoluminescence show the successful fabrication of QWWs

Multiatomic step formation on GaAs(001) vicinal surfaces during thermal treatment

Abstract We observed the surface morphology of vicinal GaAs(001) after thermal treatment in AsH 3 H 2 atmosphere by atomic force microscopy (AFM). Clear multiatomic steps were formed under the high temperature thermal treatment. Next, we investigated the mechanism of step bunching during thermal treatment by two experiments from the view point of Ga atom evaporation. One is the selective thermal treatment using a partially masked GaAs wafer, and the evaporation amount of Ga atoms was estimated by AFM. The other is the investigation of photoluminescence (PL) peak energy shifts for AlGaAs GaAs single quantum wells with a thermal treatment process at the top of the GaAs quantum well layer, compared to those without thermal treatment. These results indicate that the evaporation hardly occurs during the thermal treatment process. Therefore, step bunching phenomena on GaAs(001) vicinal surfaces during thermal treatment are probably caused by migration of the atoms detached from upside steps and their re-incorporation to downside steps.

Theoretical and experimental investigation of an electron interference device using multiatomic steps on vicinal GaAs surfaces

Abstract We propose a new, lateral surface superlattice (LSSL) type of electron interference devices, where the period of LSSL is typically 60 nm, by utilizing multiatomic steps on a vicinal GaAs(0 0 1) surface. Conductivity of the device is theoretically studied by taking the effect of randomness in the LSSL into account. We also investigate its drain and transconductance characteristics experimentally at low temperatures, and found clear oscillations in g m − V G characteristics, which were ascribed to the electron interference effect.

Ultra high vacuum scanning tunneling microscope observation of vicinal (001) GaAs surface and (117)B GaAs surface grown by metalorganic vapor phase epitaxy

Abstract We have observed the atomic arrangement on vicinal (001) GaAs surfaces and (117)B GaAs surface grown by metalorganic vapor phase epitaxy using an ultra high vacuum scanning tunneling microscope without exposure to air. Multilayer step regions and atomically flat terrace regions are alternately observed to the misorientation direction for both (001) GaAs surfaces misoriented by 2° toward [110] direction (called A-surface) and [ 1 10] direction (called B-surface). At the terrace region, c(4 × 4) reconstruction units are dominant. For B-surface, (4 × 2) and (4 × 3) like reconstruction units were observed between each monolayer step at multilayer step region, which correspond to (119)B GaAs surface. For A-surface, the reconstruction units are not clear at multilayer step region, but step-step separation is about 1.4 nm, which is close to (117)A GaAs surface. For (117)B GaAs surface, a lot of monolayer steps and (4 × 3) and (5 × 3) like reconstruction units were observed with significant undulations for whole area, which suggests that (117)B GaAs surface grown by MOVPE is thermodynamically unstable.

Ultra High Vacuum Scanning Tunneling Microscopy Observation of Multilayer Step Structure on GaAs and AlAs Vicinal Surface Grown by Metalorganic Vapor Phase Epitaxy

We observe the atomic structures at the multilayer step region on MOVPE-grown GaAs (001) vicinal surface using ultra high vacuum scanning tunneling microscopy (UHV-STM), and clarify that (4×2) or (4×3) like reconstruction units are dominant. Oxide free AlAs surfaces grown on GaAs vicinal surface are also successfully observed by UHV-STM. The reconstruction units at the multilayer step region on AlAs surface have the same units on GaAs vicinal surface. GaAs surface has the lack of dimmer rows on the terrace region just below the multilayer step region, while AlAs surface has dimmer rows even on the terrace just below the multilayer step region. GaAs layer growth leads tothe step bunching phenomenon and AlAs surface leads to the step debunching phenomenon.

Growth Behavior and Mechanism of Alkyl-Desorption-Limited Epitaxial Growth of GaAs on Exactly Oriented and Vicinal Substrates

New atomically controlled epitaxial growth, called alkyl-desorption-limited epitaxial (ADLE) growth, is studied on (001) exactly oriented and vicinal GaAs substrates. In ADLE growth, the growth rate is limited by the desorption rate of alkyl from organometals rather than by saturation of alkyl adsorption. First, the proposed ADLE growth mechanism is quantitatively confirmed by comparing a new theory of growth based on the alkyl-desorption rate equations with the experimental growth data taken on (001) exactly oriented substrates. Next, the behavior of multi-atomic steps on vicinal substrates is studied using an atomic force microscope (AFM). It is found that the multi-atomic-step heights are reduced during ADLE growth. This new phenomenon is explained by the ADLE growth mechanism.