Temperature Difference Method Research Articles

Crystal growth of cubic boron nitride by temperature difference method at ∼55 kbar and ∼1800 °C

The temperature difference method was applied to grow a large single crystal of cubic boron nitride (cBN) under ∼55 kbar and ∼1800 °C using LiCaBN2 as a solvent. The effect of supersaturation of boron and nitrogen atoms in the solvent was studied by changing the temperature difference. The observed difference of the shapes of grown cBN, which varied from a small polyhedral lump to a large hollow crystal, was qualitatively explained by the present understanding of crystal morphology in relation to supersaturation. Conversely, this experimental result suggests that the present understanding of crystal growth by solvent methods at a normal pressure is applicable for growth under very high-pressure and high-temperature conditions. The effect of temperature was also studied, and a cBN single crystal of ∼3 mm in size was obtained by choosing a suitable growth condition.

A Method for Remote Sensing the Emissivity, Fractional Cloud Cover and Cloud Top Temperature of High-Level, Thin Clouds

Abstract A methodology for retrieving the emissivity, cloud cover and cloud top temperature of high-level, thin clouds is developed and described. In the thermal infrared windows, the outgoing radiances from the earth's atmosphere contain information about cloud emissivity and cloud top temperature. This information is clearly demonstrated in the brightness temperature difference curves of two window channels. For the purpose of illustration, two window channels centered at 810 and 930 cm−1 are chosen to construct the brightness temperature difference curves for a range of cloud top temperatures. These curves vary for different cloud top temperatures, and along each of these curves the emissivity changes. The brightness temperature difference method is used in a simulation study to demonstrate the feasibility of retrieving the cloud top temperature and emissivity by the utilization of measurements in two window channels. As expected, a perfect retrieval is found imperfect measurements and ideal atmospheri...

Liquid phase epitaxy growth of GaAs: Si by temperature difference method

The LPE growth of a horizontal sliding system by temperature difference method is used to grow single and multiple layers of GaAs compounds from dilute solution. The weight ratio of Si to Ga solvent is 10−4 wt%. The growth rate, surface morphology, carrier concentration and Hall mobility are studied. Relationship between the above properties and the growth temperature and temperature different (ΔT) is also discussed. In general, the present results appear quite consistent with the diffusion limited model. The growth rate can be precisely controlled. The stability of the solid-liquid interface can be obtained in the epilayer growth at a constant temperature of the system which can avoid the effect of constitutional supercooling. Under proper control, a perfect epilayer and multiple smooth layers can be obtained.

In 1− xGaxP Bulk crystal growth and In 1− xGaxPepitaxial growth on In 1− xGaxP substrate by the temperature difference method under controlled vapor pressure

In 1− x Ga x P single bulk crystal with a size of 4×(4–5)×5 mm 2 have been reproducibly grown by the temperature difference method under controlled vapor pressure (TDM-CVP) [1–3]. For the first time, homogeneous In 1− x Ga x P epitaxial layers have been gro wn on In 1− x Ga x P substrate by TDM-CVP. The X-ray reflection topograph of an In 0.23Ga 0.77P epitaxial layer grown on an In 0.24Ga 0.76P substrate indicates that the cross-hatch patterns due to lattice misfit dislocations between the epitaxial layer and substrate have not been observed.

P-type conduction in ZnSe grown by temperature difference method under controlled vapor pressure

Electrical properties of a low-resistive and stable p-type ZnSe crystal grown by the temperature difference method under controlled vapor pressure are reported. The temperature dependence of Hall mobility, carrier (hole) concentration, and conductivity are measured by the van der Pauw method. Hole mobility appears to be about 200 cm2/V s at 100 K and about 50 cm2/V s at 300 K. The activation energy of a shallow acceptor impurity is also determined to be 70–85 meV.

Surface morphology and properties of GaAs epilayers controlled by temperature difference method of liquid phase epitaxy

Epilayers of gallium arsenide were grown by using the steady-state temperature difference method of liquid phase epitaxy. The surface of grown layers was smooth and shiny. Carrier concentrations of films varying from 1016 to 1017 cm−3 could be obtained with good reproducibility. The surface morphology growth rate, carrier concentration and Hall mobility of the epilayers were studied. Several distinct types of surface features were also investigated and explained. A segregation coefficient for the net carrier concentration versus tin concentration in the growth melt was calculated as 1·84 × 10−4 at 700°C for (100) GaAs substrate. Thickness control for epilayers down to submicron can be obtained reproducibly.

Efficiency of GaAlAs heterostructure red light-emitting diodes

Electroluminescence efficiency of GaAlAs heterostructure light-emitting diodes (LED’s) fabricated by the temperature difference method is discussed by measuring electroluminescence, carrier lifetime, and absorption coefficient of the active layer. Deep levels, distribution of carriers in the indirect valley and the reabsorption of the emitted light in the active layer contribute to the reduction of the efficiency of the red LED’s. The measured absorption coefficient of Ga0.65Al0.35As active layer is about 103 cm−1 at 6500 Å; therefore the active layer thickness should be designed to be less than about 10 μm, to minimize the reabsorption region of the emitted light. The maximum luminescence efficiency is calculated for GaAlAs double heterostructure LED’s, taking the active layer thickness and the potential barrier height into consideration.

Homogeneous (Ga,Al)P alloy grown by the temperature difference method

A method was developed to grow homogeneous (Ga,Al)P alloy using a temperatue difference liquid phase epitaxial growth technique. In this method (Ga,Al)P polycrystals were prepared at 1000 °C prior to the growth of (Ga,Al)P alloy at 800 °C, which acted as the Al source to maintain the alloy composition constant during the growth. Electron probe microanalysis showed that the grown alloy was uniform within 0.01 mole fraction. It was also possible to control the alloy composition by this growth technique. Measurements of photoluminescence of the grown layer and electroluminescence of Zn-diffused diode revealed the grown alloy was of high quality. Observed edge emission energy indicated that the band gap varied with alloy composition. The edge band emission spectra with fine structure were observed at 77 K.

Low temperature phase diagram of Ga-Al-P ternary system

The Ga-Al-P ternary phase diagram in the low temperature region below 1000°C has been experimentally obtained and calculated based on the quasi-regular model. The liquidus lines were determined at 800, 850, 950, 1000 and 1040°C by weight loss method. The solidus compositions were measured on the epitaxial layers grown by the temperature difference method at 800, 850, 950 and 1000°C. Fairly good agreement between the data and calculated results was obtained.

Liquid-phase epitaxy of ZnSe by temperature difference method

ZnSe layers were grown epitaxially on (111)ZnSe substrates in a closed tube from a Ga solution by the temperature difference method. The grown layer under the condition that the substrate temperature was 1000°C showed strong blue emission even at room temperature. On the other hand, the layer at a lower substrate temperature and that obtained by the gradual temperature lowering method looked orange to the eye at room temperature, which are related to the Zn vacancy. In conclusion the room temperature blue emission from ZnSe epitaxial layer was obtained by controlling Zn vapor pressure during the crystal growth.

Determination of the Power-Law Wind Profile Exponent on a Tropical Coast

Abstract Hourly measurements of temperature and wind speed (at 10 and 33 m) for a one-year period were made on the flat south coast of St. Croix, U.S. Virgin Islands. Values of the exponent p used in the power-law wind profile were obtained by applying criteria of Golder's (1972) nomogram, the U.S. Nuclear Regulatory Commission's (1974) temperature difference method, and Sedefian's (1980) formulation. It was found that p ranges from 0.15 for stability class A to >0.40 for class F. Thus the familiar 1/7 power law will not be useful for a tropical coast. Since expected values of p as determined from Sedefian's nomogram were in good agreement with the observations, it is recommended for use in a tropical environment.

Luminescence study of a deep level in N-free GaP light-emitting diodes

A 1.9-eV weak luminescence band observed at 77 K in nitrogen-free GaP light-emitting diodes grown by liquid phase epitaxy of Temperature Difference Method under Controlled Vapor Pressure in the vicinity of the optimum phosphorus vapor pressure has been studied. The relevant deep level has been found to act as a dominant nonradiative center at room temperature. The electroluminescence efficiency of the green emission band (555 nm at room temperature) and minority carrier lifetime are affected by this deep level. The centers which cause the 1.90-eV luminescence band are found to distribute in a p-type bulk region and also p-n interface region. It is proposed that the deep level is related to phosphorus vacancies.

Photocapacitance study of deep levels due to nonstoichiometry in nitrogen-free GaP light-emitting diodes

Photocapacitance spectra of the excitation probability of electrons (or holes) occupied in deep levels have been measured for S- and Te-doped nitrogen-free GaP light-emitting diodes grown by temperature difference method of liquid phase epitaxy under various phosphorus pressures in the vicinity of the optimum pressure (Popt ). A band at 2.00 eV observed for the diodes grown under phosphorus pressures higher than Popt is attributed to interstitial phosphorus atoms. On the other hand, bands at 2.10 and 2.20 eV which were observed, respectively, in the spectra of S- and Te-doped diodes grown under phosphorus pressure lower than Popt are attributed to complex centers of phosphorus vacancies and donors.

Irrigation Scheduling Using Crop Canopy-Air Temperature Difference

ABSTRACT AN irrigation scheduling model was developed using crop canopy-air temperature difference as the dependent variable and net radiation, relative humidity and available soil water as independent variables. This model was used to schedule irrigations on a corn crop during the 1980 growing season. Crop yield and water use was compared with that of corn grown under irriga-tions scheduled by use of electrical resistance blocks and a water balance (checkbook) method. The yield of the treatment irrigated with the temperature difference scheduling approach was not significantly different from that of other treatments. However, the water balance method and resistance method called for additional water applications of 39 and 18 percent, respectively, when compared to the temperature difference method.

Observation of dislocations in GaAs epitaxial layers

Dislocations in GaAs epitaxial layers grown by the temperature difference method of liquid phase epitaxy were observed using X-ray topography and a chemical etching technique. Dislocations in the substrates seem to react with those propagating along the two orthogonal 〈110〉 directions at the interface. The propagation of dislocations from the substrates into the epitaxial layers and the interface lattice distortion of the GaAs homojunctions were investigated using X-ray topography of cleavage surfaces.

Low temperature phase diagram of In-Ga-P ternary system

The In—Ga—P ternary phase diagram in the low temperature region, 600–800°C, in the In-rich corner has been experimentally obtained and calculated based on the quasi-regular model with the assumption of a non-ideal solid. The liquidus lines were determined at 600, 650, 700, 750 and 800°C by weight loss method. The solidus compositions were measured on the epitaxial layers grown by the temperature difference method. Fairly good agreement between the data and calculated results was obtained.

GaAs TUNNETT Diodes

The tunnel-injection-transit-time (TUNNETT) diode is operated at a high frequency and has a low-noise level compared to the IMPATT diode. The tunnel injection in a thin carrier generating region of the TUNNETT depends strongly on the electric-field intensity over 1000 kV/cm where the ionization of carriers can be neglected, leading to a higher efficiency performance than that of the IMPATT. GaAs TUNNETT diodes with p+-n and p+-n-n+ structures have been fabricated by a new LPE method (the temperature-difference method under controlled vapor pressure). The fundamental oscillation at frequencies from about 100 up to 248 GHz has been obtained from the pulse-driven p+-n-n+ diodes. This paper describes the details of the oscillation characteristics of GaAs TUNNETT diodes.

200 GHz Tunnett Diodes

The tunnel injection transit time (Tunnett) diode is expected to be the useful solid state device, because it can be operated with lower bias voltage than that of the Impatt, and with extremely low noise level in the wavelength region from millimeter to submillimeter. This paper describes the recent results of the GaAs Tunnett diode with p+ -n and p+ -n-n+ structure prepared by a new liquid phase epitaxial growth method (temperature difference method under controlled vapor pressure) and the improvement of the device fabrication technique. The fundamental oscillation frequency from 110 to 208 GHz has been obtained and the lowest pulsed input power for the oscillation was 2.1 W.

Effects of Vapor Pressure on GaP LED's

The pure green emission with high external quantum efficiency of 0.03% is reported in the GaP diodes grown by the temperature difference method under controlled vapor pressure. The emission and photocapacitance spectra show remarkable variations with phosphorus pressure. The concentrations of deep levels are suppressed by an application of the optimum phosphorus pressure. Also, in nitrogen-doped diode, it has become clear that the density and energy of nitrogen levels in GaP depend largely on phosphorus pressure applied.

Minority-carrier lifetime measurements of efficient GaAlAs p-n heterojunctions

High-efficiency Ga1−xAlxAs p-n heterojunctions have been fabricated by the temperature-difference method (ηRT, 1–3% at 6650 A), and the deep levels which govern the efficiency and the lifetime have been studied by I-V, C-V, photocapacitance, impedance, and electroluminescence measurements. The lifetime obtained by the impedance measurement and the deep-level distribution obtained by the C-V measurement have a correlation. The lifetime for efficient diodes is as low as 1 μs at 80 K. The temperature dependence of the lifetime was also measured. Photocapacitance spectra show a threshold photon energy of 0.65 eV. Arsenic vacancies are proposed for these deep levels.