Atomic-Scale, All Epitaxial In-Plane Gated Donor Quantum Dot in Silicon A. Fuhrer,* ,† M. Fu ¨ chsle, ‡ T. C. G. Reusch, ‡ B. Weber, ‡ and M. Y. Simmons ‡ School of Physics, Centre for Quantum Computer Technology, School of Physics, UniVersity of New South Wales, Sydney, New South Wales 2052, Australia Received October 21, 2008; Revised Manuscript Received December 18, 2008 ABSTRACT Nanoscale control of doping profiles in semiconductor devices is becoming of critical importance as channel length and pitch in metal oxide semiconductor field effect transistors (MOSFETs) continue to shrink toward a few nanometers. 1,2 Scanning tunneling microscope (STM) directed self-assembly of dopants is currently the only proven method for fabricating atomically precise electronic devices in silicon. To date this technology has realized individual components of a complete device with a major obstacle being the ability to electrically gate devices. Here we demonstrate a fully functional multiterminal quantum dot device with integrated donor based in-plane gates epitaxially assembled on a single atomic plane of a silicon (001) surface. We show that such in-plane regions of highly doped silicon can be used to gate nanostructures resulting in highly stable Coulomb blockade (CB) oscillations in a donor-based quantum dot. In particular, we compare the use of these all epitaxial in-plane gates with conventional surface gates and find superior stability of the former. These results show that in the absence of the randomizing influences of interface and surface defects the electronic stability of dots in silicon can be comparable or better than that of quantum dots defined in other material systems. We anticipate our experiments will open the door for controlled scaling of silicon devices toward the single donor limit. The use of hydrogen resist lithography for atomic-scale device fabrication is currently pursued by several groups for either dopant-based, 3-5 nanotube, 6 or molecular electronic 7 devices. In addition to developing atomically abrupt dopant profiles for continued silicon miniaturization, 8 the concept of patterning of donors in silicon by STM was proposed over 10 years ago for the realization of atomically precise architectures for applications in single electronics and quantum computing circuits. 4,9 Since then significant ad- vances have been made in the scientific development of sub 30 nm donor-based nanostructures for electronic transport measurements. 3,10,11 However, to date the technique has only been used to study individual components of a complete device architecture such as donor nanowires and tunnel junctions with dimensions of a few nanometers. One of the main obstacles to the broader application of this technology has been the ability to controllably gate these nanostructures. Here, we demonstrate the use of highly doped epitaxial silicon gates STM-patterned in the same plane as a quantum dot device with nm position accuracy and extremely high electronic stability. Device fabrication was performed on an Omicron variable temperature ultrahigh vacuum (UHV) scanning tunneling microscope (STM) system with phosphine and hydrogen microdosing systems and a silicon sublimation (SUSI) cell attached to it. The surface of an n-type 1-10 Ωcm silicon sample with etched registration markers was prepared for lithography by flashing to 1100 °C with direct current heating. The Si(001) surface is terminated with hydrogen, introduced through a cracker source at a pressure of 5 × 10 -7 mbar for 6 min while heating the sample at 340 °C. This hydrogen resist is then selectively removed with the STM tip by applying a sample bias V smpl ) 4-8 V and using a feedback current I 0 ) 1-3 nA. At a sufficiently high current density, the covalent bonds between the hydrogen and the surface Si atoms are broken and dangling bonds are created where the STM tip is scanned. 12 Subsequent room temperature saturation dosing with PH 3 at a pressure P ) 5 × 10 -9 mbar for 5 min and thermal incorporation of the phosphorus into the Si surface at T ) 350 °C for 1 min leads to a highly conductive phosphorus doped δ-layer (N ph ≈ 1 2 × 10 14 cm -2 ) at the surface in the areas where the hydrogen was desorbed by the STM tip. Figure 1a shows a composite filled state STM image (V smpl )-1.8 V, I 0 ) 0.1 nA) taken immediately after patterning the quantum dot structure in the hydrogen terminated silicon surface by selective hydrogen desorption with the STM. All of the active device area lie on a single monatomic terrace and appear bright in the STM-images due to a change in the electronic structure at a dangling bond site compared to the hydrogen-terminated areas. The dot in the center is connected by two 8 nm wide tunnel gaps to the source and drain terminals which have a minimum width of 4 nm (∼5 silicon * To whom correspondence should be addressed. E-mail: fuhrer@nigra.ch. † School of Physics. ‡ Centre for Quantum Computer Technology, School of Physics. NANO LETTERS 2009 Vol. 9, No. 2 707-710 10.1021/nl803196f CCC: $40.75  2009 American Chemical Society Published on Web 01/02/2009