E.D. Lu

A sulfur passivation for GaAs surface by an organic molecular, CH3CSNH2 treatment

A sulfur passivation method for GaAs, CH3CSNH2 treatment has been developed. It is quite effective for removing the surface oxide layer and forming the sulfide passivation layer on GaAs surface. The enhancements of the PL intensity reveal the reduction of the surface recombination velocity and the reduction of density of defect states by this treatment. The synchrotron radiation photoemission spectroscopy measurements show that sulfur atoms bond both Ga and As atoms. After being annealed, a stable sulfur passivation layer is terminated on the surface due to the As2S3 component react with GaAs into the GaS component.

NEUTRALIZED (NH4)2S SOLUTION PASSIVATION OF III-V PHOSPHIDE SURFACES

Synchrotron radiation photoelectron spectroscopy has been used to investigate III–V phosphide GaP and InP (100) surfaces treated with a neutralized (NH4)2S solution. Compared to the conventional basic (NH4)2S solution treatment, a thick sulfide layer with P–S bond and strong Ga–S (In–S) bond of high thermal stability is formed on the neutralized (NH4)2S-treated GaP (InP) (100) surfaces. The possible passivation mechanisms of the two (NH4)2S solutions to III–V phosphide surfaces are also discussed.

Investigation of neutralized (NH4)2S solution passivation of GaAs (100) surfaces

Synchrotron radiation photoelectron spectroscopy combined with scanning electron microscopy (SEM) and gravimetry has been used to study GaAs (100) surfaces treated with a neutralized (NH4)2S solution. Compared to the conventional basic (NH4)2S solution treatment, a thick Ga sulfide layer and strong Ga–S bond were formed on the GaAs surface after dipping GaAs wafers in a neutralized (NH4)2S solution. Gravimetric data show that the etching rate of GaAs in the neutralized (NH4)2S solution is about 15% slower than that in the conventional (NH4)2S solution. From SEM observation, fewer etching pits with smaller sizes were found on the neutralized (NH4)2S-treated GaAs surface.

The role of S passivation on magnetic properties of Fe overlayers grown on GaAs(100)

We have produced epitaxial Fe overlayers on sulfur-passivated GaAs(100) surfaces by CH3CSNH2 treatment, and investigated the correlation between magnetic properties of the overlayers and surface chemical structure of GaAs(100) surfaces by ferromagnetic resonance and synchrotron radiation photoemission. The surface chemical properties were modified by changing the annealing temperature of the surfaces prior to the growth. The results show that the magnetization of Fe overlayers is crucially determined by the presence of Ga–S chemical bonds and excess As after the anneals. A comparative investigation of the magnetization has been made on both S passivated and clean GaAs(100). It is confirmed that S passivation on the GaAs surface can effectively eliminate the magnetization deficiency previously attributed to interdiffusion of As into the Fe overlayer.

Studies of interface formation between Co with GaAs(100) and S-passivated GaAs(100)

Abstract Interface formation between Co with GaAs(100) and S-passivated GaAs(100) by CH 3 CSNH 2 treatment has been studied with synchrotron radiation photoemission. Strong interface disruption and reaction occurs between the overlayer with GaAs(100) even at low Co coverage (∼0.2 nm), while the reaction is much weaker on S/GaAs(100); a stable interface forms at a coverage of 1 nm and 0.8 nm, respectively. For S-passivated GaAs(100), Ga atoms bonded with S at the surface exchange with Co atoms and cause the formation of Co–S bonding, the amount of As bonded with Co is much less than that on GaAs(100), no segregated As appears at the surface of Co overlayer, in contrast with the case of Co/GaAs(100), indicating that S-passivation on GaAs(100) is an effective way of inhibiting the interdiffusion of As and Ga through the overlayer.

Synchrotron radiation photoelectron spectroscopy study of ITO surface

Abstract Synchrotron radiation photoelectron spectroscopy (SRPES) has been applied to surface analysis of indium tin oxide (ITO) thin films. Several different components of In and Sn were observed at the clean ITO surface. By comparing the chemical compositions of the film before and after vacuum annealing, the contents of In 2 O 3− x and Sn 3 O 4 were found to be the major factors influencing the electrical conductivity and optical transparency of the film.

Studies of Mg overlayer on GaAs(100) surface treated by CH3CSNH2

Abstract A new sulfur passivation method for GaAs, CH 3 CSNH 2 treatment, has been developed. By Synchrotron Radiation Photoemission Spectroscopy(SRPES), the chemical states and electronic aspects of the passivated surfaces are investigated. It is found that the oxide layer of the GaAs is effectively removed, and Sulfur atoms bond both to Ga and As atom at room temperature. In addition, the behavior of Mg deposited on the passivated surfaces with and without annealing has been investigated. It is found that Ga atoms can be exchanged from GaS bond, and diffuse into Mg overlayer, but the sulfur atoms remain at the interfaces. At higher Mg coverage, a MgGa alloy may be formed due to excess Mg atoms reacting with Ga atoms at the overlayer.

Growth and magnetic properties of Fe overlayer on S-passivated GaAs substrate

Abstract We have produced epitaxial Fe overlayers on S-passivated GaAs(100) surfaces by CH3CSNH2 treatment. The correlation between magnetic properties of the overlayers and surface chemical structure of GaAs(100) surfaces was investigated by changing the annealing temperature of the surface prior to growth. The results show that the magnetization of Fe overlayers is crucially determined by the GaxS chemical bonds and by the presence of excess As after the anneals. A comparative investigation of the magnetization has been performed on both S-passivated and clean GaAs(100). It is confirmed that S-passivation on GaAs surfaces can effectively eliminate the magnetization deficiency previously attributed to interdiffusion of As into the Fe overlayer.

INTERFACE FORMATION AND INTERACTION OF FE OVERLAYER ON S-PASSIVATED GAAS(100)

Abstract We have studied the interface formation and electronic structure of an Fe overlayer deposited on S-passivated GaAs(100). In the first stage of deposition, Fe clusters were formed near S atoms. Compared to Fe/GaAs(100), the sulfur passivation weakens the reaction between As and Fe. It is beneficial to the magnetism at the interface. A magnetic ordering feature could be found at higher coverage due to large exchange splitting.

Interfaces of Mg and MgOx films with GaAs(100) substrate studied by synchrotron radiation photoemission

Abstract The interaction of ultrathin Mg and MgOx films with the GaAs(100) semiconductor substrate was investigated using synchrotron radiation photoemission. The results showed that strong interaction existed between Mg and GaAs leading to the formation of an interface more than 11 A, while negligible interaction and interdiffusion took place between the MgOx overlayer and the substrate. Different Mg:O 2 ratio during the deposition gave rise to the formation of MgOx with different compositions and properties.