ArcAdiA

Ultradense phosphorus in germanium delta-doped layers

2009-03-31T22:00:00Z

Ultradense phosphorus in germanium delta-doped layers Scappucci, Giordano; Capellini, Giovanni; Lee, W. C. T.; Simmons, M. Y. 2009-04 Applied Physics Letters 94 162106 Phosphorus (P) in germanium (Ge) delta-doped layers are fabricated inultrahigh vacuum by adsorption of phosphine molecules onto anatomically flat clean Ge(001) surface followed by thermal incorporationof P into the lattice and epitaxial Ge overgrowth by molecular beamepitaxy. Structural and electrical characterizations show that P atomsare confined, with minimal diffusion, into an ultranarrow 2-nm-widelayer with an electrically active sheet carrier concentration of4x10(13) cm(-2) at 4.2 K. These results open up the possibility ofultranarrow source/drain regions with unprecedented carrier densitiesfor Ge n-channel field effect transistors.

Atomic-scale patterning of hydrogen terminated Ge(001) by scanningtunneling microscopy

2009-11-30T23:00:00Z

Atomic-scale patterning of hydrogen terminated Ge(001) by scanningtunneling microscopy Scappucci, Giordano; Capellini, Giovanni; Lee, W. C. T.; Simmons, M. Y. 2009-12 Nanotechnology 20 495302 In this paper we demonstrate atomic-scale lithography on hydrogenterminated Ge(001). The lithographic patterns were obtained byselectively desorbing hydrogen atoms from a H resist layer adsorbed ona clean, atomically flat Ge(001) surface with a scanning tunnelingmicroscope tip operating in ultra-high vacuum. The influence of thetip-to-sample bias on the lithographic process have been investigated.Lithographic patterns with feature-sizes from 200 to 1.8 nm have beenachieved by varying the tip-to-sample bias. These results open up thepossibility of a scanning-probe lithography approach to the fabricationof future atomic-scale devices in germanium.

Influence of encapsulation temperature on Ge:P delta-doped layers

2009-11-30T23:00:00Z

Influence of encapsulation temperature on Ge:P delta-doped layers Scappucci, Giordano; Capellini, Giovanni; Simmons, M. Y. 2009-12 Physical Review B 80 233202-1 - 233202-4 We present a systematic study of the influence of the encapsulationtemperature on dopant confinement and electrical properties of Ge:Pdelta-doped layers. For increasing growth temperature we observe anenhancement of the electrical properties accompanied by an increasedsegregation of the phosphorous donors, resulting in a slight broadeningof the delta layer. We demonstrate that a step-flow growth achieved atsimilar to 530 degrees C provides the best compromise between highcrystal quality and minimal dopant redistribution, with an electronmobility similar to 128 cm(2)/Vs at a carrier density 1.3x10(14)cm(-2), and a 4.2 K phase coherence length of similar to 180 nm.

N-type SiGe heterostructures for THz intersubband transitions

2008-12-31T23:00:00Z

N-type SiGe heterostructures for THz intersubband transitions De Seta, Monica; Capellini, Giovanni; Evangelisti, Florestano; Busby, Yan 2009 513-514 Research on band-gap engineering of Silicon-Germanium heterostructures for the realization of Quantum Cascade (QC) structures emitting in the Terahertz (THz) spectral region has recently attracted a vast interest. While several successful attempts have been reported using hole-based (p-type) intersubband transitions, very few results have been published on systems exploiting electrons (n-type). In this work we present the optical and structural characterization of n-type heterostructures made either of tensely-strained Si (sSi) quantum well (QW) confined between low Ge content Si1-xGex barriers [0.2

Agglomeration process in thin silicon-, strained silicon-, and silicongermanium-on-insulator substrates

2009-04-30T22:00:00Z

Agglomeration process in thin silicon-, strained silicon-, and silicongermanium-on-insulator substrates Capellini, Giovanni; Ciasca, Gabriele; De Seta, Monica; Notargiacomo, Andrea; Evangelisti, Florestano; Nardone, Michele 2009-05 Journal of applied physics 105 093525 In this paper we present a comparative study of the agglomeration process in silicon-on-insulator (SOI), silicon germanium-om-insulator(SGOI), and strained SOI (SSOI) thin layers under thermal annealing inultrahigh vacuum. In particular, we provide the first evidence and characterization of agglomeration in SGOI and SSOI substrates. A common agglomeration dynamics is observed in all the substrates investigated,with the semiconductor-on-insulator layer thickness being the main parameter governing it. These findings provide a better understanding of the surface-energy-driven dewetting phenomenon in semiconductor layers and allow us to single out the influence of the surface and stress energies on the void formation and evolution, as well as on the size and density of the agglomerated islands.

Terahertz intersubband absorption and conduction band alignment inn-type Si/SiGe multiple quantum wells

2008-12-31T23:00:00Z

Terahertz intersubband absorption and conduction band alignment inn-type Si/SiGe multiple quantum wells Ciasca, Gabriele; De Seta, Monica; Capellini, Giovanni; Evangelisti, Florestano; Ortolani, Michele; Virgilio, Michele; Grosso, Giuseppe; Nucara, Alessandro; Calvani, Paolo 2009 Phisical review B 79 085302 Absorption due to conduction intersubband transitions is studied inn-type s-Si/SiGe multiquantum wells (MQW) of different well widths andbarrier composition grown by UHV-chemical vapor deposition (CVD). Themeasured intersubband transition energies are compared with thetheoretical results of a tight-binding model which provides theelectronic band structure of the complete MQW system throughout thewhole Brillouin zone. Our findings demonstrate both the high quality ofthe CVD grown MQWs and the effectiveness of the adopted tight-bindingmodel in describing band profiles and electronic structures of SiGemultilayer systems. In particular we have evaluated the conduction bandoffsets in the investigated structures.

Conduction band intersubband transitions in Ge/SiGe quantum wells

2009-07-31T22:00:00Z

Conduction band intersubband transitions in Ge/SiGe quantum wells De Seta, Monica; Capellini, Giovanni; Busby, Yan; Evangelisti, Florestano; Ortolani, Michele; Virgilio, Michele; Grosso, Giuseppe; Pizzi, Giovanni; Nucara, Alessandro; Lupi, Stefano 2009-08 Applied Physics Letters 95 051918-051918-3 In this letter we present the experimental evidence of intersubbandabsorption in the conduction band of compressively strained germaniumquantum wells bounded by Ge-rich SiGe barriers. The measured absorptionenergies are in the terahertz range and are interpreted by means oftight binding calculations which include self-consistent band-bendingand depolarization effects. From the comparison of experimental andnumerical results a conduction band offset along the L line of about120 meV has been estimated for the studied heterostructures.

Island and wetting-layer intermixing in the Ge/Si(001) system uponcapping

2009-07-31T22:00:00Z

Island and wetting-layer intermixing in the Ge/Si(001) system uponcapping De Seta, Monica; Capellini, Giovanni; Evangelisti, Florestano 2009-08 Superlattices and microstructures 46 328-332 In this paper we present an atomic force microscopy and X-rayphotoemission spectroscopy study of the composition and shape evolutionof self-assembled Ge/Si(001) islands upon capping with Si. We foundthat the islands undergo a reverse Straski-Krastanov shape evolution,with a progressive Si-enrichment of both the wetting layer and theislands. We demonstrate that the island shape evolves at constantvolume with silicon atom incorporation occurring in the absence oflateral diffusion of Ge and Si atoms from the wetting layer to theislands themselves. (C) 2008 Elsevier Ltd. All rights reserved.