The 4 K Hall mobility has been measured in a top-gated, inverted, modulation-doped Si/Si0.8Ge0.2 structure having a Si:B doping layer beneath the alloy. From comparisons with theoretical calculations, we argue that, unlike an ordinary enhancement-mode SiGe p-channel metal–oxide–semiconductor structure, this configuration leads to a decrease of interface roughness scattering with increasing sheet carrier density. We also speculate on the nature of the interface charge observed in these structures at low temperature.

Irrigation water quantity and quality limitation is the main problem of agricultural development in the research area (Rafsanjan pistachio orchards in Iran). Optimization of the irrigation system is one of the most important factors to enhance water use efficiency in this region. This research project was designed to compare the applicability of two different types of irrigation, including traditionally used surface irrigation and a simple and relatively cheap subsurface drip irrigation (using a perforated pipe covered with plastic cloth). For this purpose two plots, each containing 39 pistachio trees and 720 m 2 in area, were selected in an orchard and were both irrigated using an exactly equal quantity and quality of water for 3 years. At the end of the second year the yield in the plots was harvested separately and compared. The ratio of the weight of fresh and also dried crop in the subsurface irrigation plot to those of surface irrigation plot was respectively 1.895 and 2 for the second year, and 2.17 and 2.12 for the third year. Another parameter measured for the trees of the two plots was annual shoot growth. The value of the plot growth index (PGI) in the surface irrigation plot was calculated as 2238 cm, whereas in the subsurface irrigation plot it was 4580 cm. In addition, the dried weight of weed grown in the surface irrigation plot was 82 kg but was only 21 kg in the subsurface irrigation plot. These results show the considerable difference in efficiency of the two irrigation systems, and relatively higher preference for a subsurface system over the traditionally used surface method.

Low-temperature electrical properties of two-dimensional hole gases (2-DHGs) in Si/Si0.8Ge0.2/Si inverted modulation-doped structures have been investigated at different hole densities using a metal semiconductor gate sputtered on top of these structures. The 2-DHG which is supplied to the inverted interface of Si/SiGe/Si quantum well by a Si boron-doped layer spatially grown beneath the alloy, was controlled in the range of 1.5–7.8×1011 cm−2 hole density by biasing the top gate. With increasing 2-DHG sheet density, the hole wave function of these structures expands and moves away from inverted interface, consequently the mobility enhances. These results may be understood theoretically by elaborating the role of interface charge, roughness, and alloy scattering mechanisms in limiting the mobility of holes at the inverted interface.