We have measured excess carrier lifetimes in GaN with various doping concentrations and surface conditions by the microwave photoconductivity decay method. GaN samples were grown by metalorganic chemical vapor deposition (MOCVD) without intentional doping and with Si doping or Mg doping on a-face sapphire substrates. By using the microwave photoconductivity decay method, we obtained 1/e excess carrier lifetimes of larger than 50 μs for the Si doped and undoped GaN and of less than 10 μs for the Mg doped GaN. We changed surface conditions for the samples by the inductively coupled plasma (ICP) etching and investigated effects of surface conditions on the carrier recombination behavior. The ICP etching has negligible effects on carrier lifetime in the Si doped GaN. On the other hand, in the undoped GaN, the ICP etching lengthened the carrier lifetime compared with the as-grown sample. On the contrary, the ICP etching shortened the carrier lifetime in the Mg doped GaN. The ICP etching seems to form hole traps and recombination centers at GaN surfaces and thus the carrier lifetime became longer in the undoped GaN and shorter in the Mg doped GaN.

Epitaxial layers of 4H-SiC are grown on (0001) substrates inclined toward <1120> and <1100> directions. Defects in these films are characterized by deep level transient spectroscopy (DLTS) in order to clarify the dependence of concentrations and activation energies on substrate inclination. DLTS results show no such dependence on substrate inclination but show thickness dependence of the concentration.

Electrical properties of PIN photodiodes fabricated on the bonded silicon on insulator (SOI) wafers annealed at 900°C for 5 seconds were evaluated in order to investigate the effect of rapid thermal annealing (RTA) on SOI wafers. Traps in the SOI layers with different thicknesses (10,30,100 μm) were investigated using the deep level transient spectroscopy (DLTS) method. In the SOI layer with a thickness of 100 μm, a trap with deep energy level (about Ec-Et=0.55 eV) was observed and the concentration of the trap decreased from 5.0 × 1011 cm−3 to 1.5 × 1011 cm−3 by RTA. For PIN photodiodes on the 100 μm-thick SOI layer, the dark current decreased from 2 × 10−9 A to 6 × 10−10 A, and sensitivity uniformity for a 35 μmφ light spot and spectral responses were both improved by RTA. Lifetimes were obtained from open-circuit voltage (Voc) decay curves for 940 nm and 655 nm light, and they increased from 37 μs to 57 μs and from 47 μs to 62 μs, respectively, by RTA. For thinner SOI layers (thickness=10, 30 μm), PIN photodiodes have good uniformity and low dark current, and their characteristics were not changed by RTA.

In this study, we evaluated the electrical properties of the bonded silicon-on-insulator (SOI) wafers with lifetime measurements using a non-contact laser-microwave method. We prepared one group that consisted of bonded SOI wafers with different active layer thicknesses (I0,30,100μm) and another group consisting of bonded SOI wafers with different buried oxide layer thicknesses(0,0.01,0.1,0.75μm). Primary mode lifetime (τ1) was measured by the photoconductivity decay (PCP) method using the laser diode (λ= 774nm) as a carrier-injected light source. Steady-state change in the conductivity was measured by the photoconductivity modulation (PCM) method using a He-Ne laser (λ = 633nm) as a carrier-injected light source. τ1 decreases as the active layer thickness decreases. The PCM intensity also decreases with decreasing active layer thickness. Surface and interface recombination rates of the SOI are increased with decreasing layer thickness. The PCM intensity also decreases as the buried layer thickness decreases.

The surface recombination of GaAs which has a high carrier concentration layer (HCCL) formed by Si+ implantation has been investigated using the reflectance microwave probe (RMP) method. The RMP method enables us to evaluate the surface property of GaAs contactlessly and easily. The experimental results of the samples which were implanted with doses ranging from 1.0×1011 to 3.9×1012cm-2 at an energy of lOOke V indicate that the effective surface recombination velocity decreases with dosage because of HCCL formed after the annealing. On the other hand, the results of the samples which were implanted with a dose of 3.9 × 1012cm-2 at energies ranging from 30 to 180keV indicate that the effective surface recombination velocity increases with energy for energies larger than 50keV. We understood the reason by comparing with the numerical calculation results of an effective surface recombination velocity at a high-low junction interface.

Highly accurate X-ray masks are strongly required to establish SR lithography technology. X-ray masks must be produced as accurately as the LSI devices, because a one-toone projection aligner system is used. To minimize the in-plane mask distortion, it is desirable to estimate the value of the stress and the non-uniformity in the membrane fabrication (SiN) process. The values of the stress were estimated from the measurement of the warpage and the calculation. It is very difficult to obtain the stress distribution in the SiN/Si wafer. Thus, we measured the minority carrier lifetime distribution using the non-contact laser/microwave method. The carrier injection was done by a 774nm or 904nm semiconductor laser diode, and their beam was focused to about 500 μmφ. The surface lifetime, τ s, of the SiN/Si wafer with the stress over ˜ 108dyn/cm2 decreased to 60–70% of that of the bare Si wafer. Thus, the contactless laser/microwave system can be adaptable for the characterization in the X-ray mask process.

We apply the reflectance microwave probe (RMP) method to characterize the surface condition of the sulfur-treated GaAs. Undoped semi-insulating GaAs wafers are dipped in (NH4)2S or (NH4)2Sx [1<x≦3] after an etching. The intensity of the reflected microwave under He-Ne laser (λ=633nm) irradiation is proportional to the excess carrier density, which strongly depends on the surface condition. The (NH4)2Sx treatment increases the RMP signal intensity, while no significant change in the signal intensity is observed after the (NH4)2S treatment. The signal intensity of the (NH4)2Sx-treated samples is decreased by the annealingyhe results observed in this study are consistent with those previously found with other measurement methods. This method will be able to in-situ evaluate the surface condition of GaAs during the device fabrication process.

A GaAs/InAs heterostructure was characterized by micro-Raman spectroscopy. A 2 μm thick GaAs layer was grown on an (100) InAs substrate by molecular beam epitaxy. The sample was then angle-lapped so that the interface region is exposed on the bevel. At the close vicinity of the interface, GaAs longitudinal-optic (LO) frequency was lower by about 3 cm−1 than at the asgrown surface. The LO shift decreased with increasing distance from the interface. The spectral width did not strongly depend on the position, and thus the shift would be mainly due to strain. A similar experiment was carried out for an InAs/GaAs structure, and a broad peak which was tentatively assigned to the plasmon-LO coupled mode was observed for the InAs layer.

Ge and Zn atoms were introduced into the unirradiated regions of Si at 150°C and GaAs wafers at 50°C, respectively by using the electron-beam doping method. The surfaces of Si and GaAs substrates were covered partially by the overlayers of Ge and Zn sheets, respectively. The only surfaces of the Ge and Zn sheets were irradiated locally. with high energy electrons at 7MeV with the fluences of 5×1017 – 1×1018 electrons cm-2 . Even at a distance of ~10mm from the irradiated overlayers in the Si and GaAs substrates, Ge and Zn atoms respectively, whose interstitials may migrate the unirradiated regions, were detected by SIMS measurements. PL signal due to band-to-acceptor (ZnGa ) transition at 1.48eV becomes observable after annealing at 800°C for 20mm in the unirradiated GaAs region, which is separated from Zn sheet by nearly 10mm.