Unusual oxidation-induced core-level shifts at the HfO2/InP interface.

X-ray photoelectron spectroscopy (XPS) is one of the most used methods in a diverse field of materials science and engineering. The elemental core-level binding energies (BE) and core-level shifts (CLS) are determined and interpreted in the XPS. Oxidation is commonly considered to increase the BE of the core electrons of metal and semiconductor elements (i.e., positive BE shift due to O bonds), because valence electron charge density moves toward electronegative O atoms in the intuitive charge-transfer model. Here we demonstrate that this BE hypothesis is not generally valid by presenting XPS spectra and a consistent model of atomic processes occurring at HfO2/InP interface including negative In CLSs. It is shown theoretically for abrupt HfO2/InP model structures that there is no correlation between the In CLSs and the number of oxygen neighbors. However, the P CLSs can be estimated using the number of close O neighbors. First native oxide model interfaces for III-V semiconductors are introduced. The results obtained from ab initio calculations and synchrotron XPS measurements emphasize the importance of complementary analyses in various academic and industrial investigations where CLSs are at the heart of advancing knowledge.

Oxidation-Induced Changes in the ALD-Al2O3/InAs(100) Interface and Control of the Changes for Device Processing.

InAs crystals are emerging materials for various devices like radio frequency transistors and infrared sensors. Control of oxidation-induced changes is essential for decreasing amounts of the harmful InAs surface (or interface) defects because it is hard to avoid the energetically favored oxidation of InAs surface parts in device processing. We have characterized atomic-layer-deposition (ALD) grown Al2O3/InAs interfaces, preoxidized differently, with synchrotron hard X-ray photoelectron spectroscopy (HAXPES), low-energy electron diffraction, scanning tunneling microscopy, and time-of-flight elastic recoil detection analysis. The chemical environment and core-level shifts are clarified for well-embedded InAs interfaces (12 nm Al2O3) to avoid, in particular, effects of a significant potential change at the vacuum-solid interface. High-resolution As 3d spectra reveal that the Al2O3/InAs interface, which was sputter-cleaned before ALD, includes +1.0 eV shift, whereas As 3d of the preoxidized (3 × 1)-O interface exhibits a shift of -0.51 eV. The measurements also indicate that an As2O3 type structure is not crucial in controlling defect densities. Regarding In 4d measurements, the sputtered InAs interface includes only a +0.29 eV shift, while the In 4d shift around -0.3 eV is found to be inherent for the crystalline oxidized interfaces. Thus, the negative shifts, which have been usually associated with dangling bonds, are not necessarily an indication of such point defects as previously expected. In contrast, the negative shifts can arise from bonding with O atoms. Therefore, specific care should be directed in determining the bulk-component positions in photoelectron studies. Finally, we present an approach to transfer the InAs oxidation results to a device process of high electron mobility transistors (HEMT) using an As-rich III-V surface and In deposition. The approach is found to decrease a gate leakage current of HEMT without losing the gate controllability.

Crystalline and oxide phases revealed and formed on InSb(111)B.

Oxidation treatment creating a well-ordered crystalline structure has been shown to provide a major improvement for III-V semiconductor/oxide interfaces in electronics. We present this treatment's effects on InSb(111)B surface and its electronic properties with scanning tunneling microscopy and spectroscopy. Possibility to oxidize (111)B surface with parameters similar to the ones used for (100) surface is found, indicating a generality of the crystalline oxidation among different crystal planes, crucial for utilization in nanotechnology. The outcome is strongly dependent on surface conditions and remarkably, the (111) plane can oxidize without changes in surface lattice symmetry, or alternatively, resulting in a complex, semicommensurate quasicrystal-like structure. The findings are of major significance for passivation via oxide termination for nano-structured III-V/oxide devices containing several crystal plane surfaces. As a proof-of-principle, we present a procedure where InSb(111)B surface is cleaned by simple HCl-etching, transferred via air, and post-annealed and oxidized in ultrahigh vacuum.

Mechanisms of Tenebrescence and Persistent Luminescence in Synthetic Hackmanite Na8Al6Si6O24(Cl,S)2.

Synthetic hackmanites, Na8Al6Si6O24(Cl,S)2, showing efficient purple tenebrescence and blue/white persistent luminescence were studied using different spectroscopic techniques to obtain a quantified view on the storage and release of optical energy in these materials. The persistent luminescence emitter was identified as impurity Ti(3+) originating from the precursor materials used in the synthesis, and the energy storage for persistent luminescence was postulated to take place in oxygen vacancies within the aluminosilicate framework. Tenebrescence, on the other hand, was observed to function within the Na4(Cl,S) entities located in the cavities of the aluminosilicate framework. The mechanism of persistent luminescence and tenebrescence in hackmanite is presented for the first time.

Oxidation of the GaAs semiconductor at the Al2O3/GaAs junction.

Atomic-scale understanding and processing of the oxidation of III-V compound-semiconductor surfaces are essential for developing materials for various devices (e.g., transistors, solar cells, and light emitting diodes). The oxidation-induced defect-rich phases at the interfaces of oxide/III-V junctions significantly affect the electrical performance of devices. In this study, a method to control the GaAs oxidation and interfacial defect density at the prototypical Al2O3/GaAs junction grown via atomic layer deposition (ALD) is demonstrated. Namely, pre-oxidation of GaAs(100) with an In-induced c(8 × 2) surface reconstruction, leading to a crystalline c(4 × 2)-O interface oxide before ALD of Al2O3, decreases band-gap defect density at the Al2O3/GaAs interface. Concomitantly, X-ray photoelectron spectroscopy (XPS) from these Al2O3/GaAs interfaces shows that the high oxidation state of Ga (Ga2O3 type) decreases, and the corresponding In2O3 type phase forms when employing the c(4 × 2)-O interface layer. Detailed synchrotron-radiation XPS of the counterpart c(4 × 2)-O oxide of InAs(100) has been utilized to elucidate the atomic structure of the useful c(4 × 2)-O interface layer and its oxidation process. The spectral analysis reveals that three different oxygen sites, five oxidation-induced group-III atomic sites with core-level shifts between -0.2 eV and +1.0 eV, and hardly any oxygen-induced changes at the As sites form during the oxidation. These results, discussed within the current atomic model of the c(4 × 2)-O interface, provide insight into the atomic structures of oxide/III-V interfaces and a way to control the semiconductor oxidation.