Sb Surface Segregation Research Articles

Crystal growth and electronic properties of ultrahigh vacuum ion-beam sputter deposited Sb-doped Si(001)2×1

High-quality homoepitaxial Sb-doped Si(001)2×1 films have been grown on p-type Si(001) substrates by ultrahigh vacuum ion-beam sputter deposition (IBSD) at temperatures Ts between 450 and 750 °C. The load-locked multichamber system is equipped with in situ reflection high-energy electron diffraction. Sputter deposition was carried out using a 1 keV Kr+ ion beam generated by a modified Kaufman-type ion source with post-extraction electrostatic ion optics. All films were 1 μm thick and deposited at a rate of 0.35 μm h−1. Results of plan-view, cross-sectional, and convergent-beam transmission electron microscopy analyses showed that as-deposited films are highly perfect with no visible defects. Sb incorporation probabilities σSb ranged from ≂0.1 at Ts=750 °C to ≂1 for Ts≤550 °C with no indication by secondary-ion mass spectrometry (SIMS) of Sb surface segregation. These σSb values are one to three orders of magnitude larger than for coevaporative Sb doping during molecular beam epitaxy where extensive Sb surface segregation is observed. A comparison of calibrated SIMS and Hall-effect measurements established that the incorporated Sb exhibited complete electrical activity. SIMS analyses also showed no detectable Kr (detection limit ≂5×1017 cm−3). Temperature-dependent (15–300 K) electron mobilities were equal to the best reported bulk Si values.

Sb surface segregation and doping in Si(100) grown at reduced temperature by molecular beam epitaxy

X-ray photoelectron spectroscopy, depth profiling with secondary ion mass spectrometry, and conductivity measurements have been performed on Sb-doped Si(100) films grown at low temperature (350 °C) by molecular beam epitaxy. The measurements reveal two important effects: (1) a significant increase in the surface segregation of Sb as the dopant concentration approaches 1×1020 cm−3, and (2) a decrease in surface segregation as the surface concentration of Sb reaches one monolayer. We believe that the presence of this monolayer of Sb is responsible for the surface segregation becoming self-limited and the associated bulk concentration exceeding 1×1020 cm−3.

Sb surface segregation during heavy doping of Si(100) grown at low temperature by molecular beam epitaxy

Sb surface segregation and doping during Si(100) molecular beam epitaxy at low temperature have been studied by depth profiling with secondary ion mass spectrometry, x-ray photoelectron spectroscopy, and conductivity measurements. We find that at a growth temperature near 320 °C complete donor activation and doping densities near 5×1020 cm−3 are obtainable. For temperatures between 320–500 °C, measurements point to the existence of distinct surface segregation regimes. For dilute surface and bulk Sb concentrations the measurements reveal a region where the surface segregation is constant and bulk and surface concentrations are linearly related. For bulk concentrations near the solid solubility limit, the surface segregation increases rapidly with increasing bulk concentration for temperatures between 350–450 °C. Finally, for Sb-saturated surfaces the surface segregation actually decreases, and doping levels exceeding the solid solubility limit are possible.

Sb periodic doping in low-temperature Si-MBE

The Sb doping during the homoepitaxial growth on Si(111) and Si(100) surfaces has been studied at temperatures of 300–600°C. There are high-temperature and low-temperature growth regimes: for the (111) orientation the transition temperature is 500°C at growth velocity of 0.3nm/s. In the first range the exponential dependence of the Sb incorporation coefficient with an activation energy of about 1.2 eV is observed. The transition to the low-temperature regime is accompanied by the change of the surface structure from Si(111)-7×7 to 1×1. In this regime the Sb incorporation coefficient tends to unity and the activation energy is about 0.1 eV. The low-temperature doping is distinguished by the decrease of Sb surface segregation and can be used to create complicated epitaxial structures with large concentration gradients. The characteristics of the doping process observed are explained by the change of the Si adatoms concentration on the growing surface.