Query: Multiple implantation and multiple annealing of phosphorus doped germanium to achieve n-type activation near the theoretical limit

Candidate papers:

abstract: Full activation of n type dopant in germanium (Ge) reaching to its solid solubility has never been achieved by using ion implantation doping technique. This is because implantation of dopants always leaves defects such as vacancy and interstitials in the Ge crystal. While implantation induced defects are electrically neutral for the most of semiconductor materials, they are electrically positive for Ge resulting in compensation of n type dopants. In this Letter, we verified that 5 x 1019 P/cm3 is the maximum active concentration, which can be fully activated in germanium "without leaving implantation damage" per implantation/annealing cycle. The repetition of implantation and annealing of phosphorous (P) with the concentration of 5 x 1019 cm 3 leads to the activation of 1 x 1020 P/cm3 close to its solid solubility limit of 2 x 1020 P/cm3.
author_names: Jeehwan Kim

Stephen W Bedell

Devendra Sadana
title: Multiple implantation and multiple annealing of phosphorus doped germanium to achieve n type activation near the theoretical limit
year: 2012

abstract: The achievement of controlled high n type doping in Ge will enable the fabrication of a number of innovative nanoelectronic and photonic devices. In this work, we present a combined scanning tunneling microscopy, secondary ions mass spectrometry, and magnetotransport study to understand the atomistic doping process of Ge by P2 molecules. Harnessing the one dimer footprint of P2 molecules on the Ge(001) surface, we achieved the incorporation of a full P monolayer in Ge using a relatively low process temperature. The consequent formation of P P dimers, however, limits electrical activation above a critical donor density corresponding to P P spacing of less than a single dimer row. With this insight, tuning of doping parameters allows us to repeatedly stack such 2D P layers to achieve 3D electron densities up to ~2 x 10(20) cm( 3)
author_names: Giordano Mattoni

Wolfgang Matthias Klesse

Giovanni Capellini

Michelle Yvonne Simmons

Giordano Scappucci
title: Phosphorus molecules on Ge(001) a playground for controlled n doping of germanium at high densities.
venue: ACS nano
year: 2013

abstract: Obtaining heavily doped n type germanium (Ge) is difficult since n type dopant activation in Ge is limited to less than 5x1019 cm 3 which is far below the solid solubility limit of phosphorus (P) in Ge. Such poor activation has limited the rectifying properties of n+/p Ge diodes. This work is aimed at understanding the challenge of forming highly rectifying n+/p diode as well as enhancing rectification of n+/p diode by using antimony (Sb) and P coimplantation process. Enhanced n+ doping of greater than 1020 cm 3 in Ge obtained by Sb/P codoping results in enhanced rectification in Ge n+/p junction diode.Obtaining heavily doped n type germanium (Ge) is difficult since n type dopant activation in Ge is limited to less than 5x1019 cm 3 which is far below the solid solubility limit of phosphorus (P) in Ge. Such poor activation has limited the rectifying properties of n+/p Ge diodes. This work is aimed at understanding the challenge of forming highly rectifying n+/p diode as well as enhancing rectification of n+/p diode by using antimony (Sb) and P coimplantation process. Enhanced n+ doping of greater than 1020 cm 3 in Ge obtained by Sb/P codoping results in enhanced rectification in Ge n+/p junction diode.
author_names: Jeehwan Kim

Stephen W Bedell

Devendra Sadana
title: Improved germanium n+/p junction diodes formed by coimplantation of antimony and phosphorus
year: 2011

abstract: Germanium is the main candidate for replacing silicon in active regions in future complementary metal oxide transistors due to: (i) its higher mobility of charge carriers that makes it able to attain higher drive current; (ii) the availability of high k materials, excellent substitutes for its unstable native oxide and (iii) its lower melting point that allows lower processing temperatures. However, a downscaling beyond 15 nm necessarily requires higher doping levels (higher than 1x10^20cm^ 3) beyond the solid solubility of most of the dopants. In particular, n type ultra shallow junctions (USJs) are the most challenging, because of the lower solid solubility and higher diffusivity of V group elements in Ge which make the required shallow doping profiles hard to achieve. For these reasons, laser thermal annealing (LTA) in the melting regime is a promising advanced activation technology of implanted dopants in Ge for USJs formation. In fact, it has a potential capability of increasing the dopant solubility as well as of confining the diffusion processes into the molten layer, whose depth can be controlled by choosing adequate energy density in turn. Thanks to this technique, donor concentration far exceeding the theoretical maximum solid solubility limits after LTA in Ge are reported in literature for implanted phosphorous and antimony, pushing the doping limits for these systems above to 1x10^21cm^ 3. Despite the above encouraging results, melting LTA on Ge doped with arsenic as well as with acceptors was still unexplored. Therefore, the aim of this work was the investigation of the LTA process applied to both the n type and p type doping of Ge after arsenic or boron implantation. In particular, experiments on diffusion, contamination, thermal stability, residual strain and clustering were performed in order to study mechanisms influencing the resulting electrical activation.
author_names: Ruggero Milazzo
title: Doping of germanium by ion implantation and laser annealing in the melting regime
year: 2015

author_names: R G N Hall
title: Electron Hole Recombination in Germanium
year: 1952

abstract: Band gap engineering of bulk germanium (Ge) holds the potential for realizing a laser source, permitting full integration of monolithic circuitry on CMOS platforms. Techniques rely mainly on tensile strain and n type doping. In this thesis, we focus on studying diffusion based phosphorus (P) doping of Ge using spin on dopants (SOD) and tensile strain engineering using freestanding micro electro mechanical systems (MEMS) like structures. Process development of a reliable SOD recipe was conducted using furnace and rapid thermal annealing, and successful doping up to 2.5 x 1019cm 3 was achieved, resulting in approximately 10x enhancement in direct gap emission. A transition in Ge direct gap photoluminescence (PL) behaviour is observed upon doping, from being quadratically dependent on excitation power to linear. We have also demonstrated that the limited doping concentration of P in Ge using SOD is not source limited, but more probably related to the diffusion mechanism. The other part of the project concentrated on Ge strain engineering. Previous works reported high tensile strain values based on freestanding MEMS like structures made of Ge, yet without embedding an optical cavity (until recently) In this project, we realize this combination by fabricating Ge micro disks as an optical cavity on top of freestanding SiO2 structures, utilizing Ge on Insulator wafers (GOI).3D computer simulations were used to understand and optimize the devices, in terms of strain and optical performance. Raman spectroscopy and PL measurements confirmed simulation results showing higher tensile strain for beams with shorter lengths, with a maximum uniaxial strain of 1.3% Splitting of light and heavy hole energy bands was observed by PL as the strain increases, agreeing with theoretical models. Direct gap sharp peak whispering gallery modes (WGMs) were confined in 3 um disks with a maximum quality factor of ~200. Two loss mechanisms could be distinguished, red shift of the absorption edge, and free carrier absorption. In order to avoid these excitation related losses, higher strain values combined with heavy n type doping are required. A possible implementation using the same GOI platform is proposed for future work.
author_names: Abdelrahman Zaher Al-Attili
title: Band gap engineering of Germanium monolithic light sources using tensile strain and n type doping
year: 2016

abstract: Density functional theory calculations are employed to gain a fundamental insight on the interaction of n type dopants such as phosphorous and arsenic with oxygen interstitials and A centers (vacancy oxygen interstitial pairs) in silicon and germanium. We propose the formation of the phosphorous vacancy oxygen interstitial and arsenic vacancy oxygen interstitial cluster in both silicon and germanium.
author_names: Alexander Chroneos

Efstratia N Sgourou

Charalamos A Londos
title: Interaction of n type dopants with oxygen in silicon and germanium
year: 2012

abstract: Electrically pumped lasing from Germanium on Silicon pnn heterojunction diode structures is demonstrated. Room temperature multimode laser with 1mW output power is measured. Phosphorous doping in Germanium at a concentration over 4x1019cm 3 is achieved. A Germanium gain spectrum of nearly 200nm is observed.
author_names: Rodolfo Camacho-Aguilera

Yan Cai

Neil Sunil Patel

Jonathan T Bessette

Marco Romagnoli

Lionel C Kimerling

Jurgen Michel
title: An electrically pumped germanium laser.
venue: Optics express
year: 2012

abstract: We review our recent research into n type doping of Ge for nanoelectronics and integrated photonics. We demonstrate a doping method in ultra high vacuum to achieve high electron concentrations in Ge while maintaining atomic level control of the doping process. We integrated this doping technique with ultra high vacuum scanning tunneling microscope lithography and femtosecond laser ablation micron scale lithography, and demonstrated basic components of donor based nanoelectronic circuitry such as wires and tunnel gaps. By repetition of controlled doping cycles we have shown that stacking of multiple Ge:P two dimensional electron gases results in high electron densities in Ge >10(20) cm( 3) Because of the strong vertical electron confinement, closely stacked 2D layers although interacting maintain their individuality in terms of electron transport. These results bode well towards the realization of nanoscale 3D epitaxial circuits in Ge comprising stacked 2DEGs and/or atomic scale Ge:P devices with confinement in more dimensions.
author_names: Giordano Scappucci

Giovanni Capellini

Wolfgang Matthias Klesse

Michelle Yvonne Simmons
title: New avenues to an old material: controlled nanoscale doping of germanium.
venue: Nanoscale
year: 2013

abstract: Germanium Blocked Impurity Band (BIB) detectors require a high purity blocking layer 10{sup 13} cm{sup 3} approximately 1 mm thick grown on a heavily doped active layer {approx} 10{sup 16} cm{sup 3} approximately 20 mm thick. Epilayers were grown using liquid phase epitaxy (LPE) of germanium out of lead solution. The effects of the crystallographic orientation of the germanium substrate on LPE growth modes were explored. Growth was studied on substrates oriented by Laue x ray diffraction between 0.02{sup o} and 10{sup o} from the {l_brace}111{r_brace} toward the {l_brace}100{r_brace} Terrace growth was observed, with increasing terrace height for larger misorientation angles. It was found that the purity of the blocking layer was limited by the presence of phosphorus in the lead solvent. Unintentionally doped Ge layers contained {approx}10{sup 15} cm{sup 3} phosphorus as determined by Hall effect measurements and Photothermal Ionization Spectroscopy (PTIS) Lead purification by vacuum distillation and dilution reduced the phosphorus concentration in the layers to {approx} 10{sup 14} cm{sup 3} but further reduction was not observed with successive distillation runs. The graphite distillation and growth components as an additional phosphorus source cannot be ruled out. Antimony {approx}10{sup 16} cm{sup 3} was used as a dopant for the active BIB layer. A reduction in the donor binding energy due to impurity banding was observed by variable temperature Hall effect measurements. A BIB detector fabricated from an Sb doped Ge layer grown on a pure substrate showed a low energy photoconductive onset {approx}6 meV) Spreading resistance measurements on doped layers revealed a nonuniform dopant distribution with Sb pile up at the layer surface, which must be removed by chemomechanical polishing. Sb diffusion into the pure substrate was observed by Secondary Ion Mass Spectroscopy (SIMS) for epilayers grown at 650 C. The Sb concentration at the interface dropped by an order of magnitude over {approx} 1.5 {micro}m. Layers grown at 550 C did not show significant Sb diffusion. Sn doped In{sub 2}O{sub 3} (ITO) was studied for use in far infrared transparent low temperature contacts for BIB arrays. It was found that {approx}100 nm of ITO deposited on Ge remains electrically conducting at 4 K and is {approx}90% transparent in the far infrared. ITO should be suitable for passivating contacts to Ge BIB arrays.
author_names: Jordana Bandaru
title: Liquid phase epitaxial growth and characterization of germanium far infrared blocked impurity band detectors
year: 2001