Structure and composition of the c(4×4) reconstruction formed during gallium arsenide metalorganic vapor-phase epitaxy

Abstract

Surfaces of GaAs (001) were prepared by metalorganic vapor-phase epitaxy and characterized by scanning tunneling microscopy, x-ray photoelectron spectroscopy, infrared spectroscopy, and low-energy electron diffraction. Upon removal from the reactor, the gallium arsenide surface exhibits a (1×2) reconstruction, which is a disordered variant of the c(4×4). The disorder arises from the presence of adsorbed alkyl groups. Heating the sample to 350 °C desorbs the hydrocarbons and produces a well-ordered c(4×4) structure. A model is proposed for the alkyl-terminated (1×2) reconstruction.

Gallium arsenide and indium arsenide surfaces produced by metalorganic vapor-phase epitaxy

“…In the large-scale STM images of the gallium arsenide (0 0 1) surface taken immediately after MOVPE, one sees a regular array of terraces, indicative of step-flow growth [10]. The step edges run parallel to the [0 1 0] crystal axis and the average step width is approximately 300 A > .…”

“…The random distribution of these species on the surface produces the apparent (1;2) reconstruction observed by STM. In a previous paper, we proposed a model for the (1;2), which consists of rows of As dimers with chain lengths of 2 or 3 [10]. Interspersed between some of the dimer chains are single arsenic atoms that are terminated with a hydrocarbon radical, such as a methyl or ethyl group.…”

“…On the other hand, the arsenic to gallium ratio does not change over this same temperature range, indicating that no arsenic desorbs below 350°C. In order to identify the adsorbates present on the surface, infrared reflectance spectra have been collected before and after annealing the sample for 10 min at 100-400°C [10]. Negative peaks at 2957, 2869 and 2926 cm\ develop as alkyl groups desorb from the surface.…”

“…This is because MOVPE growth is carried out at 10-760 Torr, where only photon-based techniques for in situ surface analysis may be used. However, we have recently developed an apparatus that integrates MOVPE reactor with an ultrahigh vacuum surface analysis system [9][10][11]. This apparatus has allowed us to characterize the structure and composition of film surfaces as they evolve during growth.…”

Phase transitions of III–V compound semiconductor surfaces in the MOVPE environment

“…For example, many compound semiconductor devices are made by metalorganic vapor-phase epitaxy (MOVPE) at pressures between 20 and 100 Torr. This process is usually operated at V/III feed ratios above 10, in order to passivate the surface with less reactive arsenic or phosphorous atoms [5]. On the other hand, a low V/III ratio is sometimes used to incorporate carbon as a p-type dopant into the GaAs film.…”