Yoshihiko Yuba

Characterization of ion beam etching induced defects in GaAs

Ion beam etching (IBE) of GaAs was carried out at an energy of 1 keV using Ar and CCl2F2 as a source gas and defect center induced by IBE was investigated by means of deep level transient spectroscopy and carrier profile measurements. From DLTS measurements, five different defect centers (electron traps) were resolved. They were distributed far beyond the ion range and showed different depth profiles. The deep distribution of IBE induced defects was also confirmed from the carrier profile measurement. Annealing at 500 °C was effective to reduce the observed defect centers but defect centers with a concentration between 1×1015 and 5×1016/cm3 still remained.

Induced Defects in GaAs Etched by Low Energy Ions in Electron Beam Excited Plasma (EBEP) System

Ion beam etching (IBE) of GaAs with a source gas of Cl2 or Ar was carried out at a low energy ranging from 5 to 130 eV by using an electron-beam-excited-plasma system, and residual defect centers were investigated by means of deep-level transient spectroscopy (DLTS). Foul kinds of defect centers labeled L1 L2, L3, L5 with activation energies of 0.31, 0.45, 0.58, 0.48 eV, respectively, were resolved. Three of them were associated with damages induced by IBE and it was found that they have different thresholds for their generation, i.e., 60, 40 and 20 eV for L1, L2 and L3, respectively. It is necessary to reduce ion energy to less than 20 eV for perfect damage-free IBE of GaAs.

Ion Beam Etching of InP. I. Ar Ion Beam Etching and Fabrication of Grating for Integrated Optics

The Ar ion beam etching (IBE) of InP has been studied in orded to clarify its applicability as a microfabrication technique for devices with submicron geometry such as integrated optics devices. The IBE rate has been determined as a function of ion energy, current density and angle of beam incidence. The crystalline quality of the etched surface has been investigated by electron beam diffraction, Rutherford backscattering and photoluminescence measurements. The etched surface has a polycrystalline phase and recovers to a single crystal after annealing at 500 C. Grating structures with a period of around 2600 A have been fabricated on an InP surface by the Ar-IBE combined with a holographic-photoresist-exposure technique.

Hall Effect Measurements of Zn Implanted GaAs

The isochronal annealing behavior of the effective surface carrier concentration and effective Hall mobility of Zn-implanted layers in GaAs has been investigated. Ion implantation has been performed with 60 keV Zn ion at various doses up to 1016/cm2 at room temperature and 400°C. An annealing stage for effective Hall mobility exsists between 600 and 700°C. After annealing at 700°C and above, ionized-impurity scattering is a dominant mechanism affecting the mobility. The highest mobility obtained is 170 cm2/V sec. The maximum effective surface carrier concentration is achieved after annealing at temperatures around 700°C. Samples implanted with doses up to 1015/cm2 show a 100% doping efficiency and those implanted with heavier doses show a saturation tendency in the effective surface carrier concentration.

Deep levels induced by high-energy boron ion implantation into p-silicon

Defects induced by B+ implantation at 0.7 MeV into n+p diodes were investigated using leakage current and deep level transient spectroscopy (DLTS). Leakage current increases drastically by implantation to a dose of more than 3×1013 cm−2. DLTS spectra reveal two hole trap levels in the shallower region than the projected range of B+. One level at 265 K (Ev+0.65 eV) is associated with point defects around dislocation kinks formed by B+ implantation to doses of more than 3×1013 cm−2. Another level at 290 K (Ev+0.67 eV) is mainly responsible for the excess leakage current. This level was, for the first time, found in p‐Si after high‐energy ion implantation followed by annealing.

Defects induced by focused ion beam implantation in GaAs

The characteristics of defects induced by Si and Ga focused ion beam (FIB) implantation in n‐GaAs have been investigated by means of deep‐level transient spectroscopy (DLTS), C–V carrier profiling, and resistance measurements. The DLTS spectra of Si and Ga FIB implanted samples annealed at temperatures up to 500 °C are apparently identical to one another and show three different electron traps with an activation energy between 0.25 and 0.6 eV. The resistance increases by more than five orders of magnitude by Si and Ga FIB implantation due to the induced defects. However, it is restored to initial values after annealing at 600 °C, except for a sample of Ga implantation with a dose higher than 1014 /cm2 . For annealing of induced defects, there are no intrinsic problems for FIB implantation with a dose lower than 1013 /cm2 .

Defect study in GaAs bombarded by low-energy focused ion beams

GaAs was exposed to focused Ga+ beams at various beam energies ranging from 100 eV to 150 keV to investigate properties of defects induced by low‐energy focused ion beams. Defect concentration and distribution profiles were measured by the deep‐level transient spectroscopy technique. It was found that the defect concentration is greatly reduced for irradiation at a beam energy below 1 keV. Defects were observed even at a depth of ≥1500 A, which is far beyond the ion range (∼15 A) for 1‐keV Ga+ . This indicates that the defect is induced by diffusion and trapping of mobile primary defects. It was also found that the defects induced by the low‐energy irradiation are easily annealed out at 600 °C, while the defects induced by the high‐energy irradiation still exist after annealing at 850 °C.

Ion Beam Etching of InP. II. Reactive Etching with Halogen-Based Source Gases

The reactive-ion beam etching (R-IBE) characteristics of InP with Cl2, CCl2F2 and CHF3 have been studied. Some R-IBE characteristics of GaAs have also been studied. The etching rate for each gas has been determined as a function of ion energy, current density and angle of indidence. The highest etching rate, around 2000 A/min, is obtained in Cl2-IBE, while the two other source gases yield an etching rate lower than that of Ar-IBE. In the case of CCl2F2-IBE, the addition of Ar is found to enhance the etching considerably. These IBE techniques are used to fabricate a grating structure with a period around 2500 A.

Laser‐irradiation effects on unencapsulated GaAs studied by capacitance spectroscopy

The effect of Q‐switched ruby‐laser irradiation on unencapsulated unimplanted bulk GaAs has been investigated by means of deep‐level transient spectroscopy (DLTS) and C‐V carrier profiling. It was found that the concentration of a deep‐level center (Ec−0.83 eV) assigned to the A center decreases considerably as a result of laser irradiation, and that no deep levels (electron traps) more than 3×1013/cm3 are induced by the laser irradiation on the uncapped surface at a power level suitable for the recrystallization of an amorphous layer produced by ion implantation. No significant change in the free‐carrier profile at a depth deeper than 1500 A from the surface was observed after the laser irradiation.

Distribution Profiles and Annealing Characteristics of Defects in GaAs Induced by Low-Energy FIB Irradiation

Distribution profiles and annealing characteristics of defects in GaAs induced by various (0.1–150 keV) energy Ga-focused ion-beam (FIB) irradiation were measured by means of deep-level transient spectroscopy and C-V carrier profiling to reveal the importance of low-energy beams for damage-free device processing. Four different electron traps were induced by the irradiation and observed at >2000 A, a depth far deeper than the ion range (about 15 A for 1 keV Ga). The defects were reduced by decreasing the ion energy and easily annealed out, and full recovery in carrier density occurred after annealing at 600°C.