Study Of Spin-on Doping Of Phosphorous On Ge And Fabrication Of Ge N+/p Shallow Junction

Germanium?Ge?is considered as the most promising candidate material for silicon-based optoelectronic integrated circuit due to its high carrier mobility,large absorption coefficient at telecom wavelength(?1,55??m?,quasi-direct band structure and the compatibility with Si architecture.Suffering from low solid solubility and fast diffusion coefficient of donors in Ge,the realization of heavily n-doped Ge and shallow Ge n+/p junction has become one of the challenges for fabrication of Ge-based devices.Targeting this issue,this thesis investigates spin-on doing?SOD?of P on Ge and facilitate shallow junction.The main work and innovations of this thesis are summarized as follows:1.Sputtering of a thin amorphous Si?a-Si?capping layer?CL?prior to SOD of P on Ge was proposed to alleviate sample surface deterioration after SOD.The required thickness of a-Si CL under SOD at the different annealing temperature?580-800°C?was studied.By comparing the AFM surface morphology after P SOD,it is found that after sputtering 3nm,6nm and 9nm a-Si CL prior to P SOD on Ge,sample surface morphology can be greatly improved after P SOD with temperature at 580°C,650??800°C,respectively.2.Spin-on doping of P on Ge with a 9-nm a-Si CL was proposed to achieve n+/p shallow junctions through rapid thermal annealing?RTA?.From SIMS depth profiles,It is found that the diffusion coefficient of P in Ge is greatly reduced by sputtering a 9nm a-Si layer on Ge.After P SOD at 800??quite a number of Si atoms have diffused into Ge surface region.These Si atoms occupy most of the vacancies in the top region of Ge leading to dramatically reduce of the diffusion coefficient of P in Ge.With this method the average doping concentration of n⁺Ge is 6.6×lO¹⁹cm^-3 and the diffusion depth of P in Ge is only?40nm,n-Ge/Al ohmic contacts were fabricated with a specific contact resistivity of 3.49×10^-6 ?·cm².The fabricated n?/p shallow junction diode without surface passivation exhibits a good rectification ratio of?10⁵ at±1.0 V.The activation energy E_a extracted from current-voltage curve is 0.64 eV suggesting domination of diffusion current in the device.3.KrF nanosecond pulsed laser annealing?PLA?of P SOD Ge obtained by RTA was proposed to increase the activation ratio of doped P in Ge.After PLA witih energy density of 400 mJ/cm²,the sample surface roughness RMS was only 1.1 nm,and P activation ratio increased from 33%to 80%.Due to consumption of Si in the sample surface region,the diffusion depth of P in Ge increased to 280 nm.The fabricated n+/p junction diode without surface passivation exhibited a good rectification ratio of?4×10⁵ at±1.0 V with a dark current density of 4×10^-4 A/cm².The effect of PLA on P SOD on Ge without a-Si CL was also investigated.After PLA with energy density of 400 mJ/cm²,the sample surface roughness RMS was 1.69 nm,the specific contact resistivity of Al/n⁺Ge contacts is about 5.51×10^-5?·cm².The fabricated n+/p junction diode without surface passivatioR shows a rectification ratio of?l0⁴ at±1.OV.