Fulin Xiong

High efficiency single quantum well graded‐index separate‐confinement heterostructure lasers fabricated with MeV oxygen ion implantation

Single quantum well AlGaAs/GaAs graded-index separate-confinement heterostructure lasers have been fabricated using MeV oxygen ion implantation plus optimized subsequent thermal annealing. A high differential quantum efficiency of 85% has been obtained in a 360-µm-long and 10-µm-wide stripe geometry device. The results have also demonstrated that excellent electrical isolation (breakdown voltage of over 30 V) and low threshold currents (22 mA) can be obtained with MeV oxygen ion isolation. It is suggested that oxygen ion implantation induced selective carrier compensation and compositional disordering in the quantum well region as well as radiation-induced lattice disordering in AlxGa1–xAs/GaAs may be mostly responsible for the buried layer modification in this fabrication process.

Hydrogen depth profiling in solids: A comparison of several resonant nuclear reaction techniques

Nuclear resonant reaction analysis (NRRA) techniques for hydrogen depth profiling in solid materials have typically used ion beams of 19F at the resonance energy of 16.44 MeV and 15N at 6.385 MeV. We report here the study of hydrogen analysis and profiles with the ^1H(^(19)F, ɑy)^(16)O reaction at the resonance energy of 6.42 MeV and investigation of the nuclear resonant reaction _1H(^(15)N ɑy)^(12)C at the resonance energy of 13.35 MeV as alternative means for hydrogen depth profiling. The results show that the method using the 6.42 MeV ^(19)F resonance has an excellent depth probe capability and moderate resolution as well as adequate sensitivity, and the method using the 13.35 MeV ^(15)N resonance provides a new tool with higher sensitivity and good depth resolution. The comparison of these four NRRA techniques under identical laboratory conditions is shown. Their characteristics and conditions of optimum utilization are discussed.

Formation of buried high-resistivity layers in InP crystals by MeV nitrogen ion implantation

We have studied the formation of buried high-resistivity layers in InP single crystals by MeV ion implantation. It was found that the implantation of MeV nitrogen ions plus subsequent thermal annealing can generate a deep burried layer with resistivity up to about 10^6 Ω cm in n-type InP crystals. This layer has exhibited implant dose dependence, high thermal stability and reproducibility over a dose range of 5 × 10^(14) − 1 × 10^(16) cm^(−2). The mechanism of insulating layer generation by implantation, based on cross sectional transmission electron microscopy (XTEM) and I–V curve measurements, as well as the application of this technique in device fabrication, will be discussed.

Influence of substrate temperature on lattice strain field and phase transition in MeV oxygen ion implanted GaAs crystals

A detailed study of the influence of substrate temperature on the radiation-induced lattice strain field and crystalline-to-amorphous (c-a) phase transition in MeV oxygen ion implanted GaAs crystals has been made using channeling Rutherford backscattering spectroscopy, secondary ion mass spectrometry, and the x-ray rocking curve technique. A comparison has been made between the cases of room temperature (RT) and low temperature (LT) (about 100 K) implantation. A strong in situ dynamic annealing process is found in RT implantation at a moderate beam current, resulting in a uniform positive strain field in the implanted layer. LT implantation introduces a freeze-in effect which impedes the recombination and diffusion of initial radiation-created lattice damage and defects, and in turn drives more efficiently the c-a transition as well as strain saturation and relaxation. The results are interpreted with a spike damage model in which the defect production process is described in terms of the competition between defect generation by nuclear spikes and defects diffusion and recombination stimulated by electronic spikes. It is also suggested that the excess population of vacancies and their complexes is responsible for lattice spacing expansion in ion-implanted GaAs crystals.

Photoreflectance, absorption, and nuclear resonance reaction studies of AlxGa1−x As grown by molecular‐beam epitaxy

The photoreflectance (PR) spectra of bulk AlxGa1−xAs alloys with x<=0.45 were studied. The observed line shapes from different samples suggest that the PR technique is very sensitive to the material quality, surface condition, and the background impurities. The energy gap derived from the PR spectra compared well to that obtained from the absorption spectra. The relationship between the energy gap and the Al mole fraction value x was established through the nuclear resonance reaction analysis. The electric field near the surface was calculated from the periodicity of Franz–Keldysh oscillations observed in many of the samples. From our analysis, we believe that the number of oscillations shown in PR spectra corresponds to sample quality, in general. We also believe that the low-field-like line shape is mainly caused by the fluctuation of Al distribution along the growth direction. An additional feature related to the impurity transition was also observed in the spectra.

Electrical and structural changes in GaAs crystals from high-energy, heavy-ion implants

Changes in electrical properties and crystal structure due to MeV, heavy-ion implants in GaAs have been studied. The electrical properties of the implanted samples were obtained by measuring I–V characteristic curves on and through implanted regions and Seebeck potential differences across implanted regions. The changes in crystal structure induced by the implants were measured using RBS channeling experiments and XTEM micrographs. The RBS and XTEM results indicated that MeV ion doses > 1 × 10^(15) ions/cm^2 amorphized the crystal structure at the end of ion range. After annealing the GaAs sample, the amorphized region returned to a crystalline state but with many defect centers. In n-type doped GaAs both Cl^(3+) and O^(3+) ions induced acceptor like centers which became inactive after rapid thermal annealing. Most of the active electrical carriers can be attributed to crystal defects.

Direct determination of Al content in molecular-beam epitaxially grown AlxGa1–xAs (0<=x<=1) by nuclear resonant reaction analysis and x-ray rocking curve techniques

The techniques of nuclear resonant reaction analysis (NRRA) using 27Al(p,gamma)28Si and x-ray rocking curve (XRC) based on double-crystal diffractometry have been utilized to determine directly the Al concentration and its depth distribution in molecular-beam epitaxially (MBE) grown AlxGa1–xAs/GaAs heterojunctions. Combination of these two methods has revealed a linear relationship between the Al mole fraction and the lattice strain. This can eliminate the need for assuming that Vegards law holds and that extrapolated elastic coefficients are accurate. The result supports that both of these two techniques provide an accurate determination of the absolute Al content and crystalline quality in AlxGa1–xAs/GaAs throughout the entire composition range (0<=x<=1) as well as profiling the Al distribution. In addition, significant depth fluctuations in the Al mole fraction in some samples have been probed by the NRRA technique as well as by the XRC. The result suggests that a reliable and accurate measurement must be undertaken to ensure the control of the required Al distribution, which is necessary for the high performance of many devices.

MeV ion beam processing of III–V compound semiconductors

MeV ion beam processing provides a very promising technology for 3-dimensional device fabrication and property modification of deeply buried interfaces; its application to III–V compound semiconductors will be presented. Using MeV oxygen ion implantation one can produce deeply buried insulating layers in n-type GaAs crystals, and induce compositional disordering in GaAs/GaAlAs superlattices. It has been employed, as a simple and promising technique, for fabricating high efficiency single quantum well GRINSCH GaAs/AlGaAs lasers. Formation of deeply buried high resistivity layers in n-type InP has also been investigated. A comprehensive study of MeV-ion-implanted InP by a variety of analytical techniques has provided a coherent picture of implanted distribution, structural transition, crystalline damage, and lattice strain in the implanted InP crystals, and has led to a good understanding of the physical processes involved in MeV ion implantation and subsequent thermal annealing. Application of MeV nitrogen ion implanted InP to laser devices will also be discussed.

MeV oxygen ion implantation induced compositional intermixing in AlAs/GaAs superlattices

We present in this letter an investigation of compositional intermixing in AlAs/GaAs superlattices induced by 2 MeV oxygen ion implantation. The results are compared with implantation at 500 keV. In addition to Al intermixing in the direct lattice damage region by nuclear collision spikes, as is normally present in low‐energy ion implantation, Al interdiffusion has also been found to take place in the subsurface region where MeV ion induced electronic spike damage dominates and a uniform strain field builds up due to defect generation and diffusion. Uniform compositional intermixing of the superlattices results after subsequent thermal annealing when Al interdiffusion is stimulated through recovery of the implantation‐induced lattice strain field, the reconstruction and the redistribution of lattice defects, and annealing of lattice damage.

Amorphization and recrystallization in MeV ion implanted InP crystals

A comprehensive study of MeV-^(15)N-ion-implanted InP by a variety of analytical techniques has revealed the physical processes involved in MeV ion implantation into III-V compound semiconductors as well as the influence of post-implantation annealing. It provides a coherent picture of implant distribution, structural transition, crystalline damage, and lattice strain in InP crystals induced by ion implantation and thermal annealing. The experimental results from the different measurements are summarized in this report. Mechanisms of amorphization by implantation and recrystallization through annealing in MeV-ion-implanted InP are proposed and discussed in light of the results obtained.