Etching of GaAs(100) Surfaces by Cl2: Quantum Chemical Calculations on the Mechanisms

Franck-Condon simulation of the photoelectron spectrum of AsCl₂ and the photodetachment spectrum of AsCl ₂⁻ employing UCCSD(T)-F12a potential energy functions: IE and EA of AsCl₂

The currently most reliable theoretical estimates of the adiabatic ionization energies (AIE(0)) from the X̃(2)B(1) state of AsCl(2) to the X̃(1)A(1) and ã(3)B(1) states of AsCl 2+, and the electron affinity (EA(0)) of AsCl(2) , including ΔZPE corrections, are calculated as 8.687(11), 11.320(23), and 1.845(12) eV, respectively (estimated uncertainties based on basis-set effects at the RCCSD(T) level). State-of-the-art ab initio calculations, which include RCCSD(T), CASSCF/MRCI, and explicitly correlated RHF/UCCSD(T)-F12x (x = a or b) calculations with basis sets of up to quintuple-zeta quality, have been carried out on the X̃(2)B(1) state of AsCl(2) , the X̃(1)A(1) , ã(3)B(1) , and Ã(1)B(1) states of AsCl 2+, and the X̃(1)A(1) state of AsCl 2-. Relativistic, core correlation and complete basis-set (CBS) effects have been considered. In addition, computed UCCSD(T)-F12a potential energy functions of relevant electronic states of AsCl(2) , AsCl (2)(+), and AsCl( 2)(-) were used to calculate Franck-Condon factors, which were then used to simulate the valence photoelectron spectrum of AsCl(2) and the photodetachment spectrum of AsCl (2)(-), both yet to be recorded. Lastly, we have also computed the AIE and EA values for NCl(2) , PCl(2) , and AsCl(2) at the G4 level and for SbCl(2) at the RCCSD(T)/CBS level. The trends in the AIE and EA values of the group V pnictogen dichlorides, PnCl(2) , where Pn = N, P, As, and Sb, were examined. The AIE and EA of PCl(2) were found to be smaller than those of AsCl(2) , contrary to the order expected from the IE values of P and As.

Synchrotron Photoemission Analysis of Semiconductor/Electrolyte Interfaces by the Frozen-Electrolyte Approach: Interaction of HCl in 2-Propanol with GaAs(100)

Perspectives of a new approach for the synchrotron photoemission spectroscopic analysis of chemical processes at solid/liquid interfaces under UHV conditions have been explored. A thin layer of HCl-2-propanol solution was frozen-in on the semiconductor GaAs(100) wafer surface by cooling the substrate to liquid nitrogen temperature after etching off the native oxide layer under N2 atmosphere. Chemical reactions induced in situ by exposure to synchrotron radiation (SR) and by stepwise heating have been monitored. Right after etching and freezing, the surface is covered by gallium chlorides with 1, 2, 3, and 4 Cl ions attached and lattice back-bonded to As atoms, as well as by elemental arsenic As0 and 2-propanol. Exposure to SR at low temperature produces surface As chlorides at the expense of As0. The GaCl3 and GaCl2 emissions diminish while GaCl is enhanced. On the other hand, heating the sample to approximately 130 K just above H2O desorption causes the thermodynamically expected reaction of AsCl3 with the substrate GaAs to form Ga chloride species and As0. Heating the sample to room temperature leaves only As0 on the surface and for gallium the content of all surface chlorides is drastically reduced. By further heating to 400 K elemental arsenic starts to desorb and the Ga chloride surface content is reduced. Using different excitation energies the depth composition of the reaction products has been monitored indicating a tendency of decreasing chlorination numbers and increasing Ga vs As chloride content toward the pristine substrate at each stage of the reaction.