Russell V. Smilgys

Initial stages of heteroepitaxial growth of InAs on Si (100)

Adsorption and desorption of In on partially and fully As‐terminated Si(100) are investigated by laser‐induced fluorescence detection and Auger electron spectroscopy using the methods of temperature programmed desorption and isothermal desorption. Desorption measurements show that As is bound to the surface more strongly than In. For In, a 2/3 order kinetic desorption mechanism is observed. This and Si Auger intensity attenuation measurements indicate a strong tendency for In to form three‐dimensional islands on the As‐terminated surface. The activation energy for In diffusion from the islands ranges from 1.5 to 1.9 eV, depending on the As coverage. The results have important implications for growth of InAs on Si(100).

AES and LEED studies correlating desorption energies with surface structures and coverages for Ga on Si(100)

Abstract Gallium interactions with silicon (100) are studied with Auger electron spectroscopy and LEED to correlate the desorption energies with surface coverages and structures in isothermal desorption experiments. Some evidence for a temperature-induced change from a Stranski-Karstanov to a Volmer-Weber growth mode between 600 and 700 K is presented. In the temperature range 800–900 K, three different kinetic regimes are observed. Between 0 and 0.5 monolayers (ML), first-order desorption is observed from a well-ordered Ga overlayer (Si : Ga 2 × 2), with a desorption energy of 2.9 ± 0.2 eV and a pre-exponential factor of 3 × 10 16 ± 1 s −1 Between 0.5 and 1 ML, first-order desorption is also observed from a well-ordered Ga layer (Si : Ga 8 × 1), but the desorption energy decreases to 2.3 ± 0.2 eV with a pre-exponential factor of to 8 × 10 12 ± 1.2 s −1 . Above 1 ML, zeroth-order desorption from Ga islands on top of an ordered Ga monolayer is observed, and the desorption energy of the combination of surface species is 2.61 ± 0.07 eV with a pre-exponential factor equal to (4±3) × 10 13 ML s −1 . It is suggested that atoms from the islands and the ordered layer are kinetically coupled, and that the islands cover too little of the surface to exhibit the bulk heat of vaporization of liquid Ga, 2.9 eV. The observed kinetic regimes are correlated with the surface structures proposed in the preceding paper.

Single-photon laser ionization time-of-flight mass spectroscopy detection in molecular-beam epitaxy: application to As4, As2, and Ga

Single-photon laser ionization time-of-flight mass spectroscopy (TOF-MS) is used to monitor fluxes of As(4), As(2), and Ga, species that are important in molecular-beam epitaxy of GaAs. With this technique, fluxes of multiple chemical species above a substrate can be measured noninvasively and in real time during conventional molecular-beam epitaxy. Additionally, the geometry of the single-photon ionization TOF-MS permits simultaneous film-growth monitoring by using techniques such as reflection highenergyelectron diffraction (RHEED). Here gas-phase arsenic and gallium beams are ionized by a single 118-nm (10.5-eV) photon and detected with a TOF-MS. The 118-nm photons are produced by frequency tripling 355-nm light from a pulsed Nd:YAG laser in Xe. With single-photon ionization, less than 0.4% ofthe As(4)(+) signal fragments to As(2)(+). Neither As(4)(+) nor As(2)(+) fragments to As(+) at 118 nm. The relative ionization probability of As(4)/As(2) at 118 nm is approximately 4:1. This technique promises to be a powerful tool for analyzing most III-V and II-VI molecular-beam epitaxy growth species.

Spin-orbit state specific laser probing of the desorption kinetics and islanding behavior of In on Si(100)

Abstract The adsorption and desorption characteristics of In on Si(100) are investigated. Laser-induced fluorescence is used to probe specific spin-orbit states of the desorbing or scattered In atoms. The sticking coefficients of both In ( 2 P 1 2 ) and In ( 2 P 3 2 ) are determined to be unity ( > 0.9). State specific desorption measurements show that the two spin-orbit states have the same desorption parameters. This indicates that both spin-orbit states originate from the same “bath” of In atoms on the surface. Isothermal desorption measurements, also using Auger spectroscopy, find that at surface temperatures below 820 K, and for coverages θ 1 2 order desorption indicates two-dimensional In islands on the surface. We observe a first order desorption only for temperatures > 820 K. For θ > 0.5 ML, desorption takes place by a 2 3 order mechanism, whereas Knall et al. report a zero order. These differences are discussed in terms of possible differences in surface diffusion rates. The 2 3 order indicates indirect desorption from three-dimensional islands in terms of possible differences in surface diffusion rates. The first order desorption energy for In from Si(100) (θ T > 820 K), is 2.5 ± 0.2 eV with a pre-exponential factor of 10 log A = 14 ± 1 (s −1 . An activation energy, for the 2 3 order regime, which is attributed to diffusion of In from three-dimensional islands onto the surface, is 1.9 ± 0.1 eV, 10 log A = 10.5 ± 0.5 log ML 1 3 s −1 ) .

Photoelectron imaging of Fermi surfaces

Abstract We describe the use of an ellipsoidal-mirror analyzer to obtain cross-sectional images of electrons photoemitted from a bulk Fermi surface. The region of the Brillouin zone that is sampled can be varied by adjusting the photon energy, allowing a complete mapping of the electron Fermi surface. This technique provides an immediate and direct visualization of the occupied electronic states and their relationship to bulk symmetries.

Vibrational distributions of As2 in the cracking of As4 on Si(100) and Si(111)

The desorption dynamics of arsenic from Si(100) and Si(111) are studied by measuring the vibrational population distributions of desorbed As2 using laser‐induced fluorescence. In these measurements a steady state flux of desorbing As2 is produced by continuously dosing a heated Si surface with a beam of As4 from a conventional molecular beam epitaxy oven. Measurements of the fluxes of As2 as a function of surface temperature suggest that the As2 may be kinetically formed in two distinct steps: The As4 first chemisorbs to form atoms on the surface which then recombine to desorb as dimers. However, there may also be direct dissociation of As4 at the hot surface. The vibrational populations of As2 (v‘=0–3) desorbed from Si(100) are Boltzmann and indicate a vibrational temperature Tv that is nearly 350 K lower than the surface temperature Ts (Tv=790±100 K vs Ts=1140 K). The vibrational populations of As2 desorbed from Si(111) are not Boltzmann, but also have an effective vibrational temperature 400 K colder t...

State‐resolved laser probing of As2 in a molecular‐beam epitaxy reactor

Results are presented on the first state‐resolved optical detection of As2 in a molecular‐beam epitaxy (MBE) reactor. Using the technique of laser induced fluorescence (LIF) on the A 1∑+u–X 1∑+g transition, the gas phase populations of vibrational and rotational states of As2 emanating from a commercial As4 oven‐cracker source are probed. A Boltzmann fit of the populations of the first four vibrations indicates that these states are thermalized to the source temperature (source: 1050±25 K; vibrations: 1020±100 K). Likewise, the rotational manifold of each vibration is consistent with thermalization at the same temperature. The sensitivity of the LIF technique is sufficient to characterize a flux of 3×1014 As2 cm−2 s−1. Therefore, the method is capable of being an in situ real‐time MBE diagnostic. Optical detection may provide complementary information to reflection high‐energy electron diffraction (RHEED) that would not otherwise be available. Future applications of this technique may lead to new insights...

A study of the GaAs–Si(100) interface using laser probing of thermal desorption kinetics

The thermal desorption kinetics of Ga from initially As‐terminated Si(100) is investigated using laser‐induced fluorescence spectroscopy. During the Ga desorption process the surface does not remain fully As terminated because a significant fraction of the initial As coverage simultaneously desorbs with the Ga. For Ga coverages ≥ 0.55±0.1 ML (1 ML=6.8×1014 atoms cm−2), Ga desorbs from As‐terminated Si initially by a fractional order kinetic mechanism. Lower Ga coverages desorb more slowly and by a first order mechanism. The results suggest that at high coverages Ga desorbs initially from islands, and then at lower coverages from a two‐dimensional (2D) layer. Based on the distinct differences between Ga desorption from bare Si(100) and the desorption of Ga from the 2D Ga/As interfacial layer, this layer is probably GaAs‐terminated Si(100). These results on the GaAs system are compared with those previously reported on the InAs system, which show that In interacts with As on Si(100) less strongly than does Ga.

Laser Probing of the Dynamics of Ga Interactions on Si(lO0)

The kinetics of desorption and scattering of Ga atoms on Si(100) surfaces are probed by laser-induced fluorescence detection of the gas phase species and by Auger analysis of the surface composition. The kinetic parameters are correlated with the structures deduced by LEED and the coverages determined by Auger spectroscopy. The binding energy of Ga on Si(100) is found to be a function of coverage, starting out at 2.9 eV at low coverages and decreasing to 2.3 eV for coverages between 0.5 and 1 monolayer (ML). Ordered growth is always observed for coverages below 1 ML, but above one monolayer the growth of islands occurs on the wellordered monolayer. The onset of island formation is a strong function of temperature. A model is proposed for the structures and energetics involved in the growth of Ga on Si(100). The results are discussed in terms of the implications for epitaxial growth of GaAs on Si.