Akio Kitagawa

Production of the midgap electron trap (EL2) in molecular‐beam‐epitaxial GaAs by rapid thermal processing

Rapid thermal processing (RTP) using halogen lamps for molecular‐beam‐epitaxial (MBE) n‐GaAs layers was investigated by deep‐level transient spectroscopy. RTP was performed at 800u2009°C for 6 s with proximity capping method. It was found that the Ec −0.82 eV electron trap (EL2) was produced by RTP. The depth profile of EL2 was flat. The spatial variations of EL2 produced by RTP were observed across the MBE layers. The EL2 concentration increased by about two orders of magnitude toward the edge from the center of the samples (∼18×16 mm2). It was thought that the spatial distribution of EL2 corresponded to that of thermal stress induced by RTP.

Effects of rapid thermal processing on electron traps in molecular‐beam‐epitaxial GaAs

Variations of deep levels in Si‐doped molecular‐beam‐epitaxial (MBE) n‐GaAs layers by rapid thermal processing (RTP) using halogen lamps were investigated by deep level transient spectroscopy. RTP was performed at 700, 800, and 900u2009°C with the face‐to‐face configuration. Native deep levels M1 (Ec−0.18 eV), M3 (Ec−0.33 eV), and M4 (Ec−0.51 eV) in MBE n‐GaAs are annealed out by RTP at 900u2009°C. The metastable electron trap N1 (Ec−0.5∼0.7 eV) and the midgap electron trap EL2 (Ec−0.82 eV) are produced by RTP at 700, 800, and 900u2009°C. Two electron traps N2 (Ec−0.36 eV) and N3 (Ec−0.49 eV) are produced by RTP at 900u2009°C. The peculiar spatial distribution of N1 and EL2 are observed across the RTP layers. In particular, the EL2 distribution is found to be a W‐shaped pattern. It is supposed that this peculiar shape of the spatial variation is consistent with that of the thermal stress induced by RTP. In addition the spatial variations of EL2 are suppressed by use of the guard ring composed of GaAs pieces, since it pre...

A comparison of deep levels in rapidly thermal-processed GaAs films grown by molecular beam epitaxy on Si and GaAs substrates

A comparative study of the rapidly thermal-processed molecular beam epitaxial GaAs grown on Si and GaAs substrates is made by deep-level transient spectroscopy (DLTS). Rapid thermal processing (RTP) was performed at 910 degrees C for 9 s with SiO2 encapsulation. In the MBE layer on Si, the traps A1 (Ec-0.65 eV) and A2 (Ec-0.81 eV) are observed in addition to the trap M1 (Ec-0.18 eV) and M4 (Ec-0.51 eV) which are also commonly present in the MBE layer on GaAs. Two traps are produced by RTP in the layer on GaAs, and one of them is identified with EL2 (Ec-0.81 eV) and another one with the activation energy of 0.49 eV is labelled NC2. On the other hand, four electron traps termed R1 (Ec-0.23 eV), R2 (Ec-0.40 eV), R3 (Ec-0.44 eV) and EL2h (Ec-0.79 eV) are produced by RTP in the layer on Si. The trap EL2h is one of an EL2 family characterised by the persistent photocapacitance quenching effect. The EL2h concentration is consistent with the EL2 concentration produced by RTP in the surface region (<0.2 mu m below the surface), but in the deeper position the EL2h concentration is different from the EL2 concentration in the MBE layer on GaAs after RTP. It is suggested that the EL2h profile produced by RTP depends on the distribution and intensity of stress in the heteroepitaxial layer.

Effects of rapid thermal processing on molecular-beam epitaxy GaAs with SiOx encapsulation

Variations of deep levels in Si‐doped molecular‐beam epitaxy (MBE) n‐GaAs layers by rapid thermal processing (RTP) were investigated by deep‐level transient spectroscopy. RTP was performed at 850, 910, and 1000u2009°C with SiOx encapsulation. Native deep levels M1 (Ec − 0.18 eV), M3 (Ec − 0.33 eV), and M4 (Ec − 0.51 eV) are annealed out by RTP at a higher temperature (1000u2009°C) compared with the case of capless RTP. Three electron traps NC1 (Ec − 0.36 eV), NC2 (Ec − 0.48 eV), and EL2 (Ec − 0.81 eV) are produced by RTP. After RTP at 850 and 910u2009°C, the concentrations of the EL2 decrease with depth from the surface and show no peculiar lateral distribution across the wafer, which is different from that of capless RTP reported previously. The formation of the EL2 is enhanced by the stoichiometry change due to the Ga outdiffusion into the SiOx film during RTP. After RTP at 1000u2009°C, the outdiffusion of the EL2 is observed near the surface. This result seems to be ascribed to the As loss, since it can no longer prev...

Redistribution of deep levels in semi‐insulating GaAs wafer by rapid thermal processing

The distributions of deep levels in semi‐insulating GaAs before and after rapid thermal processing (RTP) at 800u2009°C are obtained by the contactless measurement of the optically injected excess carrier signal height by reflectance microwave prober method. The deep levels in the liquid‐encapsulated Czochralski‐grown 2 in. GaAs wafer are redistributed by RTP, and its spatial variation shows a W‐shaped pattern along the 〈100〉 radial direction. Furthermore, the distribution of deep levels in the RTP wafer corresponds to the crystallographic slip generation pattern, which is relief of the thermal stress during RTP, examined by x‐ray topography. The redistribution of the deep levels is due to the production of the principal deep level EL2 by RTP.

Spatial Inhomogeneities in Rapidly Thermal-Processed GaAs Wafer

The spatial distributions of the midgap defect (EL2) concentration in semi-insulating liquid-encapsulated Czochralski GaAs wafers have been characterized by the contactless measurement of the optically injected carrier using reflectance microwave probe (RMP) method. The four-fold symmetrical distribution of EL2 in the (100) plane is observed in the 2 inch diameter GaAs wafer after rapid thermal processing(RTP). The deep level distribution in the RTP wafer corresponds to the crystallographic slip generation pattern obtained from x-ray topography. The correlation between the pattern of the redistributed EL2 concentration and the slip generation in the RTP wafer is suggested that the EL2 is produced by the large thermal stress during RTP. Furthermore, the distributions of EL2 center measured by the RMP method are compared with the dislocation patterns in undoped and In-doped GaAs wafers.

Diffusion of Te or Zn into GaAs from Doped SiO2 Films by Rapid Thermal Processing

The n + layers on semi-insulating liquid encapsulated Czochralski GaAs and p + layers on Si-doped n-type GaAs were formed by rapid thermal diffusion (RTD) from Te- and Zn-doped oxide films, respectively. The Zn diffusion coefficient of the RTD sample at 850°C for 6s with the heating rate of 50°C/s is about two orders of magnitude higher than that of a similar furnacediffused sample at the same temperature. In addition, Zn and Te diffusion are strongly enhanced by the high heating rate of RTD. The shallow and abrupt p + n junction in GaAs is formed by RTD of Zn with the low heating rate. This shallow p + n junction is suitable for the construction of a photodiode. It is observed that the short wavelength spectral response ( + n junction. The concentration of this trap is independent of the heating rate of RTD.

Variations of Electron Traps in MBE AlxGa1−xAs by Rapid Thermal Processing

Using deep level transient spectroscopy we have studied the variations of electron traps in molecular beam epitaxial (MBE) Al x Ga 1−x As by rapid thermal processing (RTP) using halogen lamps. RTP was performed at 700, 800 and 900 °C for 6s under a SiO 2 cap and a capless condition. It is found that during RTP the electron traps with the thermal activation energies of 0.89 and 0.99 eV are produced in Al 0.l Ga 0.9 As and Al 0.3 Ga 0.7 As, respectively. The thermal activation energies of these traps are close to the reported ones for the trap EL2 in Al x GaM 1−x As. Therefore, these traps are probably related to the trap EL2. In the RTP samples under a capless condition, the concentrations of the trap EL2 in Al x Ga 1−x As (x=0.1, 0.3) decreases from the surface to the deeper position in MBE layers, while the depth profile of the trap EL2 in GaAs is flat. It is suggested that the origin of the trap EL2 formation in Al x Ga 1−x As is different from one in GaAs.