摘要:

While the cleaving process used for semiconductor Fabry–Pe´rot lasers produces atomically abrupt mirrors, there is considerable interest in mirrors defined by etching. Depending on the etching process employed, disorder of varying nature and degree results at the semiconductor–air interface. A theoretical approach capable of quantifying the impact of such disorder on the mirror reflectivity, to which laser performance is intimately connected, is presented. The theoretical technique is time‐dependent to facilitate visualization of the scattering process and is based on a locally one‐dimensional implicit‐finite‐difference approximation to the two‐dimensional scalar wave equation with variable coefficients. Mirror disorder is described in terms of a feature depth parameter and an in‐plane correlation length. The reflectivity falls off exponentially with disorder yet is found to remain close to its unperturbed value for the disorder scale attainable with the state‐of‐the‐art etching technology. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113572

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The importance of capacitively coupled radio frequency (rf) discharges has resulted in many attempts, by experiment and by simulation, to understand the dynamics of the discharge. Because of the time varying nature of the sheath potential, the sheath region is of special interest in these plasmas. Direct measurements are reported of the sheath electric fields in a helium plasma obtained using a laser induced fluorescence method. In the interpretation of these measurements, the time dependence of the fluorescence spectrum had to be considered. The measured electric field distributions can be used to deduce sheath widths. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113573

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The incorporation of hydrogen in ZnSe:N and ZnSe:Cl films grown by gas source molecular beam epitaxy (GSMBE) using elemental Zn and H2Se as source material has been investigated. The hydrogenation behavior was found to be significantly enhanced when nitrogen was used as a dopant, and typically resulted in highly resistive films. On the other hand, Cl‐doped ZnSe films showed a hydrogen concentration at or near the background levels independent of the Cl concentration. ZnSe was also grown by conventional molecular beam epitaxy with intentionally introduced H2in order to clarify the source of the hydrogen. Significant hydrogen incorporation was observed in the MBE‐grown ZnSe:N layers only when hydrogen gas was introduced. Injection of hydrogen in excess of the amount generated during typical GSMBE experiments was found to give rise to an unambiguous increase in the hydrogen concentration, but with a hydrogen:nitrogen ratio less than that measured in GSMBE films. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113574

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effects on adhesion strength of pulsed-laser irradiation prior to film deposition, and of thermal annealing following film deposition, have been studied for gold films deposited by ion beam sputtering on polished polycrystalline alumina(Al2O3)substrates. Three different atmospheres were employed for the laser irradiations: Ar-4&percent;H2,air, and oxygen, all at 1 atmosphere pressure. A similar functional dependence of adhesion strength on laser energy density,Ed,was found for all of the gaseous environments: No change of adhesion strength forEd⩽0.5 J/cm2,maximum adhesion forEd=1.0–1.5 J/cm2,and decreased adhesion for higherEd.A pronounced increase in gold-alumina adhesion strength was achieved when the alumina substrates were irradiated in an oxygen-rich atmosphere. A post-deposition 300 °C anneal doubled the adhesion strength to ∼50 MPa, approximately 500 times the strength of untreated gold-alumina couples. The adhesion strength initially increased rapidly with annealing time but saturated for times ⩾ 1 hour. The adhesion enhancement can be attributed to the formation of a high-energy disordered alumina surface during rapid solidification following pulsed-laser melting of the near-surface region. This defective surface contains reactive sites where gold atoms can form strong bonds. The data show that these sites most effectively bond gold atoms when they are saturated with oxygen. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114231

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

As the tip in the atomic force microscope is scanned over the sample surface an image results which contains information from the sample as well as from the tip. This mainly results in an increase of the apparent size of the sample. If the tip is reasonably sharp the contribution from the tip is small. In some cases the widening still persists in spite of a very sharp tip. In this letter, a model is presented which ascribes this to the lateral forces twisting the cantilever giving an offset between the apparent point of contact and the real point of contact. This results in a shift between forward and reverse scan of the sample position in the imaging window and, if the lateral forces due to the sample and substrate are different, a change in the apparent width of the sample. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113575

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

p‐polarized 633 nm light reflection wasinsitumeasured to detect a change, if any, in optical constants of hydrogenated amorphous silicon (a‐Si:H) thin films by the application of 2 MHz ultrasonic vibration to the substrate during their plasma chemical vapor deposition (CVD). Although the vibration scarcely changed the hydrogen content ina‐Si:H films under the reaction conditions of this study, it increased both the refractive index and absorption coefficient ofa‐Si:H. The results are attributable to the densification of amorphous network structure as well as to the increase of density of extended states in the valence and conduction bands. Films with improved photoconductivity were obtained by the ultrasonic vibration assisted plasma CVD. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114284

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Results from optically detected cyclotron resonance (ODCR) studies of electron effective masses in 4H SiC are reported. ODCR measurements were performed on high‐purityn‐type 4H SiC epitaxial layers grown by chemical vapor deposition at bothXband (9.23 GHz) andQband (35.05 GHz) microwave frequencies. Electron effective masses in 4H SiC were directly determined asm⊥*=0.42m0andm∥*=0.29m0. A scattering time in the basal plane &tgr;⊥≊4.3×10−11s, and hence, the corresponding electron mobility &mgr;⊥≊1.8×105cm2/V s, was obtained from a fit of the ODCR line shape. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113576

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report record high electron mobility in modulation‐doped Si/SiGe. Samples grown by ultrahigh vacuum chemical vapor deposition (UHV‐CVD) with mobility values in the range of 3.2–5.2×105cm2/V s have been measured at 0.4 K. The current and temperature dependence of the magnetoresistance in those samples have been examined and the scattering times are deduced from these measurements. At high magnetic field (≳10 T), fractional quantum Hall filling factors have been observed, and the corresponding activation energies have been calculated. These are significantly larger than previously reported values in Si/SiGe, and are comparable to those in GaAs/AlGaAs modulation‐doped heterostructures with mobility higher than 1×106cm2/V s. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113577

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The growth of highly strained InxGa1−xAs (x≳0.25) epilayer on GaAs (001) undergoes a two‐dimensional–three‐dimensional (2D‐3D) growth mode transition beyond a critical thickness which depends on the strain. We show that the growth mode is controlled by the island‐edge diffusion carrier which originates from elastic energy relaxation at the edge of 2D island. The 2D‐3D growth mode transition depends upon whether or not a new layer nucleates on top of the island of 2 ML height before coalescence. The In atoms on the surface arising from surface segregation affect the island‐edge diffusion barrier and nucleation, leading to a 3D growth mode at the critical thickness. The experimental investigation is explained satisfactorily. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113578

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report on the dc characteristics and microwave performance of AlGaN/GaN heterostructure field effect transistors in the temperature range from 25 to 300 °C. At temperatures above 200 °C, we observe the temperature activated shunt conductance which is independent of the gate voltage (the activation energy is 0.505 eV). The cutoff frequency and the maximum frequency of oscillations vary from 22 and 70 GHz at 25 °C to 5 and 4 GHz at 300 °C, respectively. The gate leakage current in the range of gate biases from −4 to +1 V is small and nearly proportional to the gate voltage even at 300 °C. At temperatures above 200 °C, the gate leakage current is temperature activated (the activation energy is 0.88 eV). These results show that deep traps strongly affect the AlGaN/GaN characteristics at elevated temperatures. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113579

出版商:AIP    

年代:1995

数据来源: AIP