| dc.description.abstract |
In this thesis, impurities doped in silicon and ZnO substrate via ion implantation method are conducted for strain stability retention under thermal treatment in strained silicon and P-type ZnO thin films formation with cocktail implantation method.
Since non-equilibrium method, ion implantation, is employed for exceeding the equilibrium solubility and generating larger enough strain in pseudomorphically silicon carbon alloy, strain stability retention in this metastable state in silicon plays a key role for further application. With High resolution X-ray diffractometer, it is found that significant strain relaxation occurs in the highly phosphorus doped concentration, 5*1014 ions/cm2, sample (CP3) under post-annealing thermal treatment, but almost full(adv.) strain stability retains in carbon only (C only) and in lower phosphorus doped concentration samples (CP1 and CP2) under same post-annealing thermal treatment. Even though strain stability retention is affected by the highest phosphorus doped concentration, it is found from dynamics simulation that strain relaxation is proportional to phosphorus doped concentration in only bulk region, not effectual in surface region. In surface region, only significant strain relaxation appears in CP3 sample and little strain relaxation arises in the rest of samples, indicating there is another strain stability retention factor in the surface. From Fourier transform infrared spectroscopy, the characteristic peaks of substitutional carbon at ~607cm-1, transition Si-C at ~705cm-1, and β-SiC at ~810cm-1 do not apparently change. In contrast, the oxygen-related peak area evolution trend is in correspondence with strain relaxation evolution in surface region. Furthermore, it is observed that the highest phosphorus doped concentration promotes the surface oxidation and facilitates oxygen diffused into bulk from SIMS and HF pretreatment prior to post-annealing facilitates the strain stability retention via removed surface oxide. From Hall measurement, only the electrical properties can be obtained in as-grown samples, but the sheet resistance becomes so high that it is overflow for all post-annealing samples.
Based on the results of high resolution X-ray diffractometer, Fourier transform infrared spectroscopy and Hall measurement, it is determined that implanted phosphorus and oxidation via post-annealing are two main factors for strain relaxation and that the volume compensation with good gettering ability of substitutional carbon is the only probably strain relaxation mechanism. Finally, new process flow is proposed for strain stability retention in phosphorus doped SiC alloy for N-MOSFETs fabrication.
Native N-type ZnO substrate is always obtained caused by the formation of donor-like defects, which have lower formation energy, during ZnO growth, but the formation of P-type ZnO substrate is required for overcoming the efficiency limitation of light emitted by ZnO homojunction. Specific ion implantation dosage is utilized for P-type ZnO thin films formation through cocktail implantation method. It is found that mono-doped ZnO by nitrogen implantation results in slight N-type conductivity under thermal activation. Dual-doped ZnO thin film with a N:P ion implantation dose ratio of 4:1 is found to be P-type under certain thermal activation conditions. Higher hole concentration (2.34*1019cm-3) can be achieved in dual-doped ZnO co-implanted with additional oxygen under a wider thermal activation window. It is more convincing P-type ZnO formation by observing a slight rectifying behavior with P-ZnO: (NPO at 600℃)/ N-ZnO (as-grown) homojunction. From high resolution X-ray diffractometer and X-ray photoelectron spectroscopy, we can find that substitutional nitrogen, NO, and substitutional nitrogen molecular, (N2)O, in N1S spetrum are at ~397eV and ~399eV respectively. It elucidates the increasement of lattice constant following the nitrogen implantation since nitrogen molecular exists and dominates the lattice constant. Moreover, the observed P-type conductivities are results of the promoted formation of PZn-4NO complex acceptor defects via the concurrent substitutional of nitrogen at oxygen sites and phosphorus at zinc sites. The enhanced solubility and the stability of acceptor defects in oxygen co-implanted N:P dual-doped ZnO film are related to the reduction of oxygen vacancy defects at the surface. It demonstrates the prospect of the formation of stable P-type ZnO thin film through cocktail implantation with specific implantation dosage. | en_US |