Beam Flux Ratio Research Articles

High quality zinc sulfide epitaxial layers grown on (100) silicon by molecular beam epitaxy

ZnS films were successfully grown by molecular beam epitaxy on (100) Si substrates. These high quality films, grown at a substrate temperature of 340 °C with a molecular beam flux ratio of Zn to S of unity, exhibited high crystallographic quality and revealed a flat surface. Secondary ion mass spectroscopic analysis showed that the film contained little impurity. In photoluminescence, a broad peak was observed at 2.6 eV at room temperature while an additional sharp peak at 3.6 eV appeared at 77 K. The latter is considered to be band-to-band emission and the former may be due to the Cu-blue emission.

Properties of AlxGa1−xAs (xAl≂0.3) grown by molecular-beam epitaxy on misoriented substrates

The effects of substrate misorientation on the morphological and optical properties of AlxGa1−xAs (xAl≂0.3) grown by molecular-beam epitaxy (MBE) have been studied. The substrate temperatures and V/III beam-flux ratios used were such that layers grown on nominally (100) substrates typically exhibited rough morphologies and poor 4.2 K PL characteristics. By intentionally misorienting the substrate slightly from (100), smooth layers can be grown at 620 and 650 °C at typical MBE growth rates (≂1 μm/h). These smooth layers also exhibited sharp, exciton-related emission peaks at 4.2 K with half-widths as narrow as 5 meV. Since rough surfaces may lead to poor interfaces between GaAs and (Al,Ga)As and in turn to degraded performance in heterojunction devices, the present results may have significant implications for the performance of such structures grown by MBE.

Reflection high-energy electron diffraction intensity oscillation study of Ga desorption from molecular beam epitaxially grown AlxGa1−xAs

Reflection high-energy electron diffraction (RHEED) intensity oscillations are used as an in situ probe to study Ga desorption during molecular beam epitaxial growth of AlxGa1−xAs. A simple thermodynamic model is developed which, in the limit of low As4 : group III beam flux ratios, accurately predicts the measured changes in AlxGa1−xAs growth rate and composition due to Ga desorption at elevated growth temperatures. The desorbing Ga flux is observed to be less in thin epitaxial layers of GaAs growing on top of AlGaAs than in bulk GaAs, giving rise to a growth rate transient at heterointerfaces.

Control of Be diffusion in molecular beam epitaxy GaAs

After molecular beam epitaxy GaAs is grown at 585 °C, substantial diffusion of Be occurs during growth of subsequent layers or during subsequent in situ annealing at 700 °C. By using an order of magnitude larger As4 flux than commonly used during growth and annealing, we were able to lower the Be diffusion coefficient by an order of magnitude. We also show that the Be diffusion coefficient is strongly dependent on the Be concentration. Different specimens were prepared with varying Be doping density, As4:Ga beam flux ratio, and annealing temperature. In these experiments, the Be concentration profiles were measured by secondary ion mass spectrometry and from them Be diffusion coefficients were calculated.

Influence of growth conditions and alloy composition on deep electron traps of n-AlxGa1−xAs grown by MBE

Two dominant deep electron traps, named ME3 and ME6, in Si-doped AlxGa1−xAs grown by MBE have been studied by Deep Level Transient Spectroscopy (DLTS) and photoluminescence measurements. The change of the two trap concentrations with growth conditions and alloy composition, and the effects of them on photoluminescence intensity are described. The ME3 concentration shows strong alloy composition dependence and has a maximum nearly equal to the doping concentration at x of about 0.4. The ME3 concentration depends linearly on the doping concentration. The ME6 concentration depends strongly on the growth temperature above 720 °C. Group V/III beam flux ratio dependence of ME6 is less than the growth temperature dependence. The growth temperature and beam flux ratio dependences of ME3 are opposite to those of ME6. ME3 has no effect on photoluminescence intensity at room temperature, whereas ME6 reduces the photoluminescence intensity.