Abstract
Single and multiple period modulation-doped (Al,Ga)As/GaAs heterostructures have been grown by molecular beam epitaxy (MBE) and characterized by Hall measurements. The basic structure consists of alternating layers of undoped GaAs and doped (Al,Ga)As separated by undoped ’’intrinsic’’ layers of (Al,Ga)As. The thickness of each of these layers was varied independently in a one, three, or nine period structure. Mobilities as high as 211 000, 95 500, and 8 360 cm2V−1 s−1 were obtained at 10 K, 78 K, and 300 K, respectively. The total sheet charge concentrations were about 2.25×1012 cm−2 in the highest mobility structures. Single period structures with an AlAs mole fraction of 0.33 typically had higher room-temperature mobilities while multiple period structures with an AlAs mole fraction of 0.2 gave better results at cryogenic temperatures. The enhanced mobilities are attributed to the separation of electrons and donors by the undoped (Al,Ga)As layers and the high quality interfaces obtainable by MBE. To our knowledge, these results on single and multiple period structures are comparable to the best values reported to date.
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