I. Camlibel

Effects of thermal annealing on semi‐insulating undoped GaAs grown by the liquid‐encapsulated Czochralski technique

Recently, a number of studies have reported a correlation between variations in threshold voltage of field effect transistors and the nonuniformity of the luminescence efficiency of semi‐insulating GaAs crystals grown by the liquid‐encapsulated Czochralski technique. The changes in luminescence efficiency and subsequently the variations in threshold voltages were dramatically reduced by postgrowth annealing of the GaAs crystals under a variety of conditions. In this study, we employ the technique of spatially resolved cathodoluminescence (CL) to carefully examine the changes in luminescence efficiency due to postgrowth annealing. In agreement with previous work, we find that the CL variations are greatly reduced from a factor of ∼2 to ∼5% by thermal annealing at 800 °C for 30 h or at 1200 °C for 6 h followed by slow cooling. The latter thermal treatment is the same as that experienced by crystals during growth by the horizontal gradient freeze (HGF) technique. The extremely uniform luminescence efficiency...

Direct evidence for the role of gold migration in the formation of dark‐spot defects in 1.3‐μm InP/InGaAsP light‐emitting diodes

The results of our previous study of dark‐spot defects (DSD’s) in aged 1.3‐μm InP/InGaAsP light‐emitting diodes (LED’s) have strongly suggested that the defects form as a result of the migration of gold from the p contact into various epitaxial layers. To provide further support for this degradation mechanism, we compare, in this study, the formation of DSD’s in LED’s fabricated with the usual BeAu p metallization and a new platinum p contact. After accelerated aging (200 °C junction temperature, 20 kA/cm2, 3×103 h), DSD’s were observed only in the devices with BeAu contacts, thus directly identifying the active role of gold migration in DSD formation.

Borosilicate clad fused silica core fiber optical waveguide with low transmission loss prepared by a high‐efficiency process

A method for making fused silica core‐borosilicate clad optical fiber waveguides is described. The process involves the growth of a needlelike layer of borosilicate glass onto the surface of a commercially available high‐purity fused silica rod by an efficient flame reaction of boron and silicon hydrides with oxygen. The needlelike layer is subsequently heat treated at relatively low temperature to form a homogeneous bubble‐free glass with a smooth surface. It is then covered with a thin protective jacket of silica and drawn into a fiber. These fibers have attenuation coefficients only slightly greater than the bulk loss of the fused silica core materials. Over the Al1−xGaxAs injection laser wavelength range, 0.82–0.88 μm, the loss is 5 dB/km, while at the YAG : Nd laser wavelength, 1.06 μm, it is 3 dB/km. The process appears to be attractive for the economical manufacture of low‐loss fibers due to its simplicity and high chemical conversion efficiency.

Anthraquinoide red display cells

Anions of anthaquinones can form highly colored salts reversibly in response to an applied potential. These electrochromic materials may be used in display devices that have good stability and an efficiency as high as 250 cm2/C. Some cells can be color modulated at less than 0.10 V. Others have a sharp threshold for color modulation near 1.5 V and may be suitable for multiplexing.

Optical aging characteristics of borosilicate clad fused silica core fiber optical waveguides

Very low transmission loss fiber optical waveguides have been developed during the past two years which have pure fused silica cores surrounded by borosilicate glass claddings. A recent study of the binary borosilicate glass system revealed that the low refractive index values which can be achieved with this glass and which are essential for the fiber cladding application occur only when the glass is quenched. Annealing causes the refractive index to increase to a less acceptable value. Although fibers are naturally quenched during drawing, there is a legitimate concern that the cladding might spontaneously anneal at its operating temperature in an unacceptably short time. The details of the annealing time−temperature relationship are determined in the present work and effective lifetimes for borosilicate clad fibers are predicted. It is concluded that lifetimes in excess of 100 years should be expected if the fiber operating temperature does not exceed 60 °C.

An experimental display structure based on reversible electrodeposition

Films of halide complexes of silver can be electrodeposited onto, or removed from, transparent indium tin oxide contacts in less than 10 msec using a clear liquid mixture of dimethyl sulfoxide (DMSO), silver halide, alkali metal halide, and bromine or iodine. The solutions do not attack the contacts, even at high voltages, as long as adequate silver remains in solution. Variations include a mulled mixture of an opacifier and superionic conductor particles in a variety of organic solvents. The electro‐optic properties of experimental display structures are discussed.

Evaluation of silicon films as a diffusion mask and encapsulant for InP and GaAs

We have determined that silicon films have nearly ideal properties for use as a diffusion mask and encapsulation coating for InP and GaAs. The Si films, composed of a single element, are easily and reproducibly deposited by electron beam evaporation at low temperatures. Sharp features can be defined by standard photolithography and freon‐plasma etching. The thermal coefficient of expansion of silicon nearly matches that of InP and GaAs so that problems due to film stress are avoided. Additionally, the interaction of Si with InP and GaAs crystals, under severe thermal treatments often used in device fabrication, was found to be negligible. Finally, we found that the Si film acts as a good diffusion mask for Zn which is a common p‐type impurity for forming p‐n junctions in III‐V compounds.

Influence of ambient media on the out‐diffusion of S from InP:S

Liquid‐encapsulated Czochralski‐grown InP:S samples annealed for short times of 30 min in various ambients at 550 °C show diffusion fronts suggesting an extremely rapid out‐diffusion of S. In phosphorus ambient, the effective diffusion coefficient is inversely proportional to the phosphorus vapor pressure. Such a strong dependence on phosphorus vapor pressure is at variance with the generally accepted substitutional‐interstitial model. The out‐diffusion is fastest in vacuum, followed by hydrogen and forming gas mixtures. In inert gas medium (He), it is substantially slower. Annealing in air suggests the rapid formation of an oxide mask with little or no out‐diffusion. An Arrhenius plot of the temperature dependence of the diffusion coefficient D in vacuum anneals, yields a D of 4×105 exp(−2.16 eV/kT) in the temperature range of 350–500 °C. Anneals in vacuum at 450 °C with different orientations showed that the out‐diffusion is nearly orientation independent except for the observed absence of diffusion fro...

Extremely rapid out diffusion of sulfur in InP

During sealed ampoule annealing of n‐type (S,Se,Sn) InP crystals at 550 °C, an unexpected diffusion front was observed whose apparent diffusivity exceeded that of the rapidly diffusing Zn impurity by about two orders of magnitude. Using luminescence techniques, this diffusion front was correlated with changes in the ionized impurity level. In this letter, we show that for annealed InP:S (2×1018 cm−3) crystals the donor profile obtained from cathodoluminescence (CL) intensity measurements corresponds to the 34S profile obtained by secondary ion mass spectroscopy. Although dislocations are generally paths along which impurities can rapidly migrate, CL imaging shows that dislocations impede rather than enhance sulfur out diffusion. Further study is required to determine the rapid out‐diffusion mechanism.

A technique for making low-loss fused silica core-borosilicate clad fiber optical waveguides

Abstract A technique for producing low-loss fused silica core-borosilicate clad fiber optical waveguides is described. The method consists of depositing radially oriented needles of borosilica on the outside surface of a fire-polished fused silica rod. This deposition is accomplished by a flame reaction of boron and silicon hydrides with oxygen. The deposit is subsequently sintered at approximately 1000°C to form a bubble free glass cladding. A thin fused silica outer jacket is then developed on this cladding to enhance the strength and the composite structure is drawn down to a fiber.