摘要:

Using contactless electroreflectance at room temperature, we have nondestructively evaluated the band bending (carrier-type) at the surface of epitaxialn- andp-type GaN/sapphire samples as well as at both the InGaN surface and the InGaN/GaN interface of samples of epitaxial InGaN, having averagen- andp-type character, grown on top of thick GaN epilayers/sapphire. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120991

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

InAs/GaP semiconductor quantum dots (QDs) were spontaneously formed using direct island growth (Volmer–Weber) rather than Stranski–Krastanow (S-K) growth. Structural investigations of InAs/GaP QDs suggest kinetically limited growth and show a broad size distribution. Photoluminescence and cathodoluminescence spectroscopy reveal large inhomogeneous broadening with the emission peak centering at 1.7 eV. Device applications exploiting broad optical emission in QDs are discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121070

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We investigated the lasing mechanism of an InGaN/GaN/AlGaN multiquantum well (MQW) laser diode on SiC grown by low-pressure metalorganic vapor phase epitaxy. Surface emission and edge emission are compared by optical pumping on the laser chip for which electrical pumping was made. Excitation power dependence of photoluminescence (PL) and PL mapping are also taken on the same chip. From the results, we demonstrate that lasing phenomena in our laser are dominated by free carriers and that the observed various stimulated emission lines are caused by the inhomogeneity of the InGaN MQW. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121436

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have investigated thermal donor formation at 450 °C in oxygen-rich SiGe with more than 1&percent; Ge content by Hall measurements and infrared spectroscopy. These measurements prove the presence of double donors in annealed Si-rich SiGe samples. The ionization energies of the donors correspond to those of the thermal double donors in Si, only the formation rate is reduced. Due to alloy effects, we observe only broadbands in the low-temperature infrared absorption spectra in SiGe instead of individual lines of neutral and singly ionized thermal donors in Si. The shift of these absorption bands to lower energies with longer heat treatment and a corresponding decrease of the ionization energy found from Hall measurements indicates the formation of shallower donor species. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121055

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We study the origins of conductivity and low-frequency noise in GaNp-njunctions under reverse bias. Carrier hopping through defect states in the space charge region is identified as the main mechanism responsible for low bias conductivity. Threading dislocations appear the most likely source of such defect states. At higher bias hopping is supplemented with Poole–Frenkel emission. A relatively high level of1/f-like noise is observed in the diode current. The bias and temperature dependencies of the noise current are investigated.©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121056

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Narrow, dry, deep-etched GaAs/GaAlAs quantum wires with modulation doping are investigated by electronic Raman scattering (RS) and far-infrared magnetotransmission (FIR). Laterally-confined plasmon and magnetoplasmon dispersions and intensities lead to the determination of the confinement potential and the free and trapped electron densities. Free electrons are observed down to a critical widthwc,significantly smaller under strong illumination (RS,wc=50nm) than in dark conditions (FIR,wc=130nm). The induced changes of the external confining potential and lateral electron distribution are analyzed in terms of a semiclassical electrostatic approach. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121057

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

GaN/SiC heterojunction diodes have been fabricated and characterized. Epitaxialn-type GaN films were grown using metalorganic chemical vapor deposition (MOCVD) and electron cyclotron resonance assisted molecular beam epitaxy (ECR-MBE) onp-type Si-face 6H-SiC wafers. TheI–Vcharacteristics have diode ideality factors and saturation currents as low as 1.2 and10−32A/cm2,respectively. The built-in potential in the MOCVD- and ECR-MBE-grownn-pheterojunctions was determined from capacitance–voltage measurements at 2.90±0.08 eV and 2.82±0.08 eV, respectively. From the built-in potential the energy band offsets for GaN/SiC heterostructures are determined at&Dgr;EC=0.11±0.10eV and&Dgr;EV=0.48±0.10eV. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121058

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Bi-layered ferroelectricSrBi2Ta2O9(SBT) films were successfully prepared onPt/SiO2/SiandPt/Ti/SiO2/Sisubstrates at 550 °C by plasma-enhanced metalorganic chemical vapor deposition. A BTO (Bi4Ti3O12orBi2Ti4O11) phase formed at the interface between SBT films andPt/Ti/SiO2/Siduring the SBT deposition at 550 °C. The BTO phase decreased the leakage current density of the SBT films. The leakage current densities of SBT films deposited onPt/Ti/SiO2/SiandPt/SiO2/Sisubstrates were about5.0×10−8and5.0×10−7 A/cm2at an applied field of 300 kV/cm, respectively. The SBT films were controlled by Schottky emission. The Schottky barrier heights of SBT films deposited onPt/Ti/SiO2/SiandPt/SiO2/Siwere about 1.2 and 0.8 eV, respectively. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121059

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present an experimental observation of the transition of different indirect tunnelling processes inp-type HgCdTe. The results demonstrate that the indirect tunnel currents via Shockley–Read–Hall traps exhibit a transition from thermally assisted tunneling to two-step indirect tunneling over a temperature range of 25–200 K, which enables independent measurements to be made on the two processes. A 55 meV trap level which contributes strongly to the indirect tunneling mechanisms was estimated by measuring the activation energy. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121054

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The induction of 90° magnetic domains in aNd2Fe14Bhard magnet has been mapped at high spatial resolution using off-axis electron holography. Line profiles from the reconstructed phase image established an upper limit for domain wall width of 10 nm. Thermal annealing resulted in domain wall movement, magnetization rotation, and evidence for pinning at a structural defect. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121060

出版商:AIP    

年代:1998

数据来源: AIP