Temperature-dependent growth mechanisms of CaF2 on Si(111)

Abstract

Temperature-dependent morphology evolution of the submonolayer clusters grown on fcc metal (110) surfaces J.The molecular-beam epitaxy of CaF 2 layers on Si(111) substrates was studied in the temperature range between 370 and 700°C. A strong temperature dependence of the CaF 2 surface morphology was found. Layer-by-layer growth modes were found in two temperature ranges: (i) between 430 and 490°C, where growth of atomically flat CaF 2 epilayers occurred, and (ii) at ϳ700°C, where a step flow mode resulted in a relatively smooth CaF 2 surface containing some rough regions, possibly due to the thermal decomposition of the interface layer. At ϳ540°C, the triangular island shape observed at lower growth temperatures changed to a more hexagonal shape expected for thermodynamic equilibrium, but the top monolayer islands still exhibited a triangular shape, which can be attributed to a relatively higher lateral adatom impingement rate per unit length of island perimeter. The mechanisms of the complex temperature-dependent growth behavior are discussed in detail.

Negative differential resistance of CaF2/Si double barrier resonant tunneling diodes fabricated using plasma etching mesa isolation process

“…One possible reason of the layer thickness deviation is the chemical reaction between Si and CaF 2 at the heterointerface for the first CaF 2 growth at a temperature of 650 °C. [25][26][27][28][29][30] Also, the experimental current densities at the voltage deviate from the peak voltage are larger than the calculated values. This is because the calculated values do not include the leakage currents due to the pinholes or defects of the barrier layers and the surface states on the mesa side wall.…”

Formation routes and structural details of the CaF1 layer on Si(111) from high-resolution noncontact atomic force microscopy data

“…A small number of studies have been performed using atomic force microscopy, most of them in contact mode [34,[60][61][62]. Recently, Klust et al presented materialdependent [63] as well as atomically resolved [64] data using in vacuo frequency-modulated NC-AFM, identifying the CaF 1 and CaF 2 areas and revealing the atomic lattice with similar contrast as has been observed before on (111) surfaces of CaF 2 crystals [65,66].…”

“…1). First, type-A films below a thickness of about 5 triple layers have been found to undergo a transition to type-B epitaxy at higher temperatures [27,29,30,34]; the in-plane crystallographic axes of the CaF 2 film are rotated by 180 • relative to the Si(111) substrate in this type-B epitaxial mode [35]. In particular, the equivalent 112 CaF 2 directions of the CaF 2 lattice and the equivalent 112 Si directions of the silicon substrate are antiparallel in type-B epitaxy as sketched in Fig.…”

“…Nakayama et al [55,56] investigated defect structures within the CaF 1 interface layer grown on Si(111) and suggested that the depressions imaged in STM are formed by clusters of excess Si atoms. Further studies focused on the morphology of submonolayer and multilayer films, where different growth modes and morphologies from varying the substrate temperature during deposition or measurement could directly be imaged [34,37,[57][58][59].…”

Scanning tunneling microscopy study of CaF2 on Si(111): observation of metastable reconstructions

“…On the other hand, if CaF 2 /Si is annealed after deposition or if CaF 2 is deposited at higher substrate temperatures, F:Ca ratio changes and becomes 1:1 for temperatures above 550 • C [9, [14][15][16], indicating desorption of fluorinated species. As a result, the morphology of the deposited films is modified as well [9,15,[17][18][19][20].…”