Kazuhisa Fukuda

Study of the deep level related to a platinum-dihydrogen complex in Si by capacitance transient spectroscopy under uniaxial stress

We have applied a novel technique to combine isothermal deep-level transient spectroscopy (DLTS) with the application of uniaxial compressive stress to studying the structure of a platinum- and hydrogen-related defect, which has a gap state at 0.14 eV below the conduction band in Si. The application of 〈100〉 and 〈111〉 stresses split the DLTS peak of the defect into two components with intensity ratios of 2.3:1 and 1.1:1, respectively, which were ratios of short- to long-time components. Under 〈110〉 stress, the peak split into three components with an intensity ratio of 0.8:3.7:1. Comparing this splitting pattern to the piezospectroscopic theory of Kaplyanskii, we have uniquely determined that the defect has the orthorhombic symmetry with the C2v point group, and have identified the defect as the Pt-H2 complex previously identified by Uftring et al. [Phys. Rev. B 51 (1995) 9612]. We also observed that the defect was reoriented above 80 K along the applied uniaxial stress. Such reorientation occurred only when the defect level was not occupied by an electron. Our observation strongly suggests that the local motion of hydrogen around the Pt atom is remarkably affected by the charge state of the defect.

High-power operation of inner-stripe GaN-based blue-violet laser diodes

We review our recent progress in novel planar blue-violet laser diodes (BV-LDs). The planar BV-LDs are characterized by an inner-stripe waveguide formed with a buried AlN current-blocking layer and a wide regrown cladding layer that also acts as a current and heat spreader. These features enable high-power operation for BV-LDs thanks to their low electrical and low thermal resistance even with a narrow-stripe waveguide. In this paper, we report successful demonstration of the planar inner-stripe BV-LDs by utilizing low-temperature-grown AlN and the regrown cladding layer. Low electrical resistance of the regrown cladding layer was confirmed by scanning spread resistance microscopy. Heat spreading characteristics were also investigated by 2-dimensional thermal simulation. The fabricated BV-LDs with a 1.4-&mgr;m-wide stripe achieved a low threshold current of 32 mA, a low threshold voltage of 4.1 V and greater than 200- mW kink-free output power under CW operation. Moreover, the kink-free output level surpassed 1,000 mW for the 1.0- &mgr;m stripe BV-LDs under 0.03%-duty-pulsed operation. The BV-LDs operated stably for more than 1,000 hours at a high output power of 200 mW at 80oC under a 50%-duty-pulsed condition. After the reliability test, transmission electron microscopy revealed no defect near the regrown interface of the tested LDs.

Stress-Induced Level Shift of a Hydrogen–Carbon Complex in Silicon

We have studied the stress-induced shift of a deep level at Ec-0.15 eV due to a hydrogen-carbon complex in Si using deep-level transient spectroscopy (DLTS) under uniaxial compressive stress. Linear stress dependencies of the ionization energy of the above level were observed for five components of split DLTS peaks altogether for , and stresses. By subtracting the stress shifts of conduction band minima from the stress dependencies of ionization energy, the net stress shifts of the energy level were obtained. Two piezospectroscopic parameters, A1 and A2, were determined as approximately 4 and -9.5 meV/GPa, respectively. Considering a molecular-orbital schematic suggested here and throughout, we conclude that the stress-induced level shifts and the split pattern of DLTS peaks reflect the trigonal symmetry and antibonding character of the electronic state of the complex. These properties are completely consistent with the atomic configuration in which a hydrogen atom occupies the bond-centered site between Si and C atoms.

Isotope Effects on the Dissociation of a Hydrogen-Carbon Complex in Silicon

We have found, by deep-level transient spectroscopy (DLTS), that the dissociation rate of a deuterium-carbon complex in silicon is about half that of a hydrogen-carbon complex, while the activation energies for the dissociation of both the complexes are the same. This clearly proves that both the complexes have the same atomic configuration and their dissociation is governed by the atomic jump of hydrogen (deuterium).

Comparative Study of Electronically Controlled Motion of Hydrogen around Carbon and Platinum Atoms in Silicon

We have studied the local motion of hydrogen in the neighborhood of carbon and platinum impurities by observing the stress-induced reorientation and subsequent recovery of two H-related (H-C and Pt-H2) complexes in Si, using deep-level transient spectroscopy (DLTS) under uniaxial compressive stress. We notice two interesting differences in hydrogen motion around carbon and platinum atoms. The first one is a difference in the temperature where stress-induced reorientation occurs. That of the H-C complex occurs at high temperatures above 250 K, while it occurs at low temperatures around 80 K for the Pt-H2 complex. The second difference is the effect of charge state of the complexes on their stress-induced reorientation and subsequent recovery. It occurs preferentially when an electron occupies the level of the H-C complex, but the Pt- H2 complex has the reverse effect of level occupancy. These differences are discussed from viewpoint of different atomic configurations and electronic states of two H-related complexes.