Combined Theoretical And Experimental Studies On The Production And Control Of Color Centers In Semiconductor

The past two decades have seen intensive research efforts aimed at creating quantum technologies that leverage phenomena such as coherence and entanglement to achieve device functionalities surpassing those attainable with classical physics.While the range of applications for quantum devices is typically limited by their cryogenic operating temperatures.Recently,point defect in semiconductors have emerged as potential candidates for room temperature quantum technologies.In particular,the nitrogen vacancy?NV?center in diamond has gained prominence for the ability to measure and control its spin under ambient conditions and its potential applications in magnetic field sensing.The NV center has been shown to be a very promising candidate as an individually addressable,solid-state qubit for quantum computing,as a single-photon source for quantum communication,and as high-precision quantum sensor for magnetic field,electric field,strain field,and even inertia and rotation.For the various applications as a high precision sensor,the compact ensemble of the high density NV centers in diamond is required.For instance,it has been evaluated that,for sensing inertia and rotation a quantum gyroscope fabricated on an 1 mm³ diamond crystal with the NV center density of 1 × 10¹⁸ cm^-3 outperforms the best available gyroscope based on the micro-electro-mechanical systems technology.Here,we describe experiments that produce the NV centers in diamond and estimated it concentration by photoluminescence,electron spin resonance and positron annihilation spectroscopy.The electron irradiation at room temperature and at 77 K,high-temperature annealing and silicon ions implantation diamond were used to produce high-density NV in our research.It is shown that electron irradiation diamond at room temeperature or 77 K can significantly enhance the NV centers formation.The high-temperature annealing diamond powder also enhance the NV centers formation.But the silicon ions implantation diamond decrease the NV center formation.Considering diamond is not yet a technologically mature material,and processing techniques are still being developed,fabrication devices on diamond is very difficult.In addition,studying defects with attributes similar to those of the NV center may help to shed light on some of the properties of the NV center that are not yet fully understood.In our studies,an isoelectronic center with NV center in diamond,such as NV center in 3C-SiC,O-V center in 4H-SiC were studied by experiment and theoretical calculation.We also studied the defect which was different with NV center in diamond,like the negatively charged state silicon vacancy in 4H-SiC.To understand the spin and optical properties,we used the Franck-Condon approximation to calculate the spin-conserved optical transition,which was important to manipulate the photon-induced electron transition between the ground state and the excited state of defect center.And then,we estimate the electron spin coherence time of the defect center,which is important for spin coherent manipulation and qubit operation.The calculation employed a simple scheme combining the mean-field theory and the first-principles calculations,according to the uncertainty principle,the electron spin coherence time was obtained.We also explore other defect center in very wide semiconductor,which are semiconductors with bandgap energies rougly 2.0 or larger.The transition metals in MgO might play an important role as they can form color centers MgO and can be intentionally doped or ion implanted in MgO.In our studied,the divalent substitional Ni impurity has been propsed to qubit application with long spin coherence time.In our research,we view of the diamond,SiC and MgO materials for qubit application by experimental and theoretical calculation.In this thesis we focus on:?1?how to improve the concentration of NV color centers in diamond;?2?Which type of defects in silicon carbide as a candidate for qubit application;?3?As a candidate for qubit application in others materials.Below are the main results and conclusions.?1?Electron irradiation ?b-type diamond at room temperature and low temperature can effectively produce NV color center,and electron iiradiation ?a-type diamond mainly produce vcancy-type defects.Compared the electrn irradiation at room temperature with low temperature,it is found that the low temperature electron irradiation is the same effectively to produce NV centers in diamond with room temperature.?2?The optical signal of NV^-1 center in diamond is tempereature-dependent,when the temperature down to the 5 K,the optical signal of NV^-1 center in diamond is obvious improved,and the optical signal of NV⁰ center in diamond is obvious decreased.It is indicated that the low temperature can effective convert NV⁰ center to NV^-1 center in diamond.?3?Vacancy-type defects in silicon carbide have met the requirement of the qubit application,such as the NV center in 3C-SiC,which shared many properties with NV center in diamond.The VSi and V_SiO_C centers in 4H-SiC also have met required of the qubit application,and the electron irradiation and ion implantation in 4H-SiC can effectively produce the Vsi and VSiOc centers.?4?The divalent nickel-doped cubic magnesium oxide is met the required of the qubit application,and the spin-conserved optical transition energy is lower than NV center in diamond.The spin coherence times is in an order of second at T=0 K.Moreover,it is elucidated that the Ni ion implantation can effectively produce the Ni_Mg⁰ center in MgO.