Chemistry of arsenic incorporation during GaAs/GaAs(100) molecular beam epitaxy probed by simultaneous laser flux monitoring and reflection high-energy electron diffraction

Abstract

Transmission electron microscopy and reflected high-energy electron-diffraction investigation of plastic relaxation in doped and undoped ZnSe/GaAs (001) Arsenic incorporation during GaAs/GaAs͑100͒ molecular beam epitaxy is studied in situ with laser single-photon ionization time-of-flight mass spectrometry and reflection high-energy electron diffraction ͑RHEED͒. Incident and scattered fluxes of Ga and As n species in front of the growing GaAs wafer are ionized repetitively by a pulsed laser beam of 118 nm ͑10.5 eV͒ photons. The methods to obtain and interpret time-of-flight mass spectra and the simultaneous RHEED measurements are described. The real time behaviors of incident Ga and desorbing As 2 and As 4 , obtained without mass spectral cracking, are studied during growth of GaAs layers with As 4 and when growth is arrested as a function of substrate temperature and Ga/As 4 flux ratio. During growth only with As 4 , both As 2 and As 4 are desorbed or scattered in varying amounts depending on flux and substrate temperature conditions. Without an incident gallium flux, desorbing As 4 decreases while desorbing As 2 increases with increasing surface temperature. During gallium deposition and GaAs growth, the amounts of desorbing arsenic fluxes decrease linearly with increasing Ga/As 4 flux ratio, but the arsenic incorporation rate saturates at a Ga/As 4 flux ratio у2, i.e. ͑Ga/Asу 1 2 ͒. The total integrated incorporation of arsenic increases linearly with increasing Ga/As 4 flux ratio when the surface is allowed to recover with an incident arsenic flux after the gallium flux is terminated. In the range of substrate temperatures optimum for layer-by-layer GaAs growth with As 4 , As 4 incorporation dominates at low temperatures, while As 4 and As 2 incorporations contribute equally at high temperatures. Surface reaction sequences and mechanisms of arsenic incorporation are discussed and compared with measured RHEED results and previous experimental and theoretical results.

Desorption of Arsenic Species during the Surfactant Enhanced Growth of Ge on Si(100)

“…The desorption or scattering of As n species from Ge/Si(100) surfaces during the surfactant enhanced epitaxy of Ge on Si(100), as well as desorption of As n species from Ge(100) and Si(100) surfaces, both under a continuous flux of As 4 , is studied using single-photon time-of-flight mass spectrometry. These experiments are conducted in a home-built ultrahigh vacuum (UHV) chamber described in detail previously . This chamber, with a base pressure of ∼5 × 10 -11 Torr (∼7 × 10 -9 Pa), is equipped with Auger electron spectroscopy (AES) to probe the chemical composition of the surface, an Ar + sputter gun for surface cleaning, a quadrupole mass spectrometer, reflection high energy electron diffraction (RHEED) to determine surface structure, and a single-photon ionization time-of-flight mass spectrometer (SPI-TOFMS) to probe the gas-phase species above the sample, either in the incident beam or the scattered or desorbed products.…”

“…The 9th harmonic is generated by tripling 355 nm light (∼35 mJ/pulse at 100 Hz, 5 ns duration, generated by tripling the 1064 nm light in standard nonlinear crystals) in a static gas cell containing approximately 5 Torr of xenon. The 355 nm light is focused into the gas cell using a quartz lens, and the resulting 118 nm photons (from the four wave mixing process) are collimated using a LiF lens and enter the UHV chamber through a LiF window . The conversion efficiency of this process is estimated to be 1 × 10 -5 . , The 118 nm photons enter the chamber and propagate parallel to the substrate and intersect the gaseous species about 1 cm in front of the growing wafer.…”