Desorption characteristics of selenium and tellurium thin films

Abstract

The temperature-dependent desorption behavior of selenium and tellurium is investigated using a heated quartz crystal microbalance. Prior to heating the quartz crystal microbalance, selenium and tellurium films with varying thickness were deposited using thermal effusion cells in a molecular beam epitaxy system for subsequent determination of temperature-dependent mass loss of the deposited films. The desorption rate for tellurium was found to exhibit one sharp peak around 190 °C, indicating the loss of the entire film irrespective of film thickness within a temperature window of 20 °C, which was completely evaporated at 200 °C. Similar experiments for selenium revealed that the thermal desorption took place via a two-stage process with a smaller portion of the material desorbing within an even narrower temperature window of 5 °C at a much lower peak temperature of 65 °C, while most selenium desorbed within a temperature range of 10 °C around 90 °C. This two-stage behavior indicated the presence of at least two chemically distinct selenium species or binding states. The direct and quantitative determination of the chalcogen desorption process provides important insights into the kinetics of chalcogenide-based film growth and is in addition of applied benefit to the research community in the area of Se/Te capping and decapping of air sensitive materials as it provides temperature ranges and rates at which full desorption is achieved. Our work furthermore points toward the need for a more detailed understanding of the chemical composition state of atomic and molecular beams supplied from thermal evaporation sources during growth.

Growth of Nanometer-Thick γ-InSe on Si(111) 7 × 7 by Molecular Beam Epitaxy for Field-Effect Transistors and Optoelectronic Devices

“…Additionally, the higher flux ratio generally led to thicker films as more Se could incorporate into the film. The direct transition of mixed-phase In 2 Se 3 –InSecategory Ito In-rich InSecategory IIIcan be related to a sharp drop of the Se sticking coefficient, which was reported earlier for pure Se deposition at much lower temperatures. , At even higher temperatures around 400 °C, no film growth was observed on the Si surface, suggesting that both Se and In had a nearly zero sticking coefficient at these growth temperatures.…”

“…The direct transition of mixed-phase In 2 Se 3 − InSe�category I�to In-rich InSe�category III�can be related to a sharp drop of the Se sticking coefficient, which was reported earlier for pure Se deposition at much lower temperatures. 51,52 At even higher temperatures around 400 °C, no film growth was observed on the Si surface, suggesting that both Se and In had a nearly zero sticking coefficient at these growth temperatures. Surface morphologies of single-phase InSe films investigated with AFM are shown in Figure 4.…”

Self-limiting stoichiometry in SnSe thin films

“…The sticking coefficient of selenium at the growth temperatures is effectively zero. 30 The theory results indicate that the excess selenium forms clusters that translate across the surface. These selenium clusters are weakly interacting with the SnSe film, leading to the stabilization of a 1 : 1 SnSe stoichiometry as film growth progresses.…”

“…There is a high volatility of selenium and a low sticking coefficient, leading to constant reentrant growth. 30 Supplying an excess of a volatile component has been shown to be useful in maintaining stoichiometry in some lead and bismuth containing compounds, but this method works best when there is a mechanism of self-limiting stoichiometry. For example, it has been shown in Bi 4 Ti 3 O 12 and Bi 2 Sr 2 CuO 6 thin films deposited by MBE that a surplus of bismuth doesn't affect composition due to the low sticking coefficient of bismuth and the evaporation of the different phases at deposition temperatures.…”

“…There is a high volatility of selenium and a low sticking coefficient, leading to constant reentrant growth. 30…”