Real Substrate Temperature Research Articles

Proper In deposition amount for on-demand epitaxy of InAs/GaAs single quantum dots**Project supported by the National Key Basic Research Program of China (Grant No. 2013CB933304), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB01010200), and the National Natural Science Foundation of China (Grant No. 65015196).

The test-QD in-situ annealing method could surmount the critical nucleation condition of InAs/GaAs single quantum dots (SQDs) to raise the growth repeatability. Here, through many growth tests on rotating substrates, we develop a proper In deposition amount (θ) for SQD growth, according to the measured critical θ for test QD nucleation (θc). The proper ratio θ/θc, with a large tolerance of the variation of the real substrate temperature (Tsub), is 0.964−0.971 at the edge and > 0.989 but < 0.996 in the center of a 1/4-piece semi-insulating wafer, and around 0.9709 but < 0.9714 in the center of a 1/4-piece N+ wafer as shown in the evolution of QD size and density as θ/θc varies. Bright SQDs with spectral lines at 905 nm–935 nm nucleate at the edge and correlate with individual 7 nm–8 nm-height QDs in atomic force microscopy, among dense 1 nm–5 nm-height small QDs with a strong spectral profile around 860 nm–880 nm. The higher Tsub in the center forms diluter, taller and uniform QDs, and very dilute SQDs for a proper θ/θc: only one 7-nm-height SQD in 25 μm2. On a 2-inch (1 inch = 2.54 cm) semi-insulating wafer, by using θ/θc = 0.961, SQDs nucleate in a circle in 22% of the whole area. More SQDs will form in the broad high-Tsub region in the center by using a proper θ/θc.

相分離系コバルト―酸化インジウム酸化スズ薄膜を用いたスパッタ中の基板表面温度評価

The real substrate temperature during sputtering was estimated by adopting a phase separation system of cobalt-indium tin oxide thin film. The nanostructure, consisting of Co fibers in an In2O3-SnO2 (ITO) matrix was formed during sputtering through surface diffusion. The increase of the substrate surface temperature was determined based on sputtering time and substrate temperature dependence of the Co fiber diameter. The activation energy of mutual surface diffusion was determined as being 0.57 eV using values of the real substrate temperature. The increase of real substrate temperature due to the increase of power density was also estimated.

High Quality&amp;lt;tex&amp;gt;$rm SmBa_2rm Cu_3rm O_7hbox -delta$&amp;lt;/tex&amp;gt;Thin Films on&amp;lt;tex&amp;gt;$rm SrTiO_3$&amp;lt;/tex&amp;gt;

We for the first time report a successful fabrication of a high-J/sub C/ SmBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(SmBCO) thin film (/spl sim/240 nm thickness) on SrTiO/sub 3/ (100) substrate by the pulsed electron beam deposition (PED) process. For this study, we systematically investigated the effect of processing parameters, including substrate temperature (Ts), ambient oxygen pressure (PO/sub 2/), and target-to-substrate distance, on superconducting properties, including critical temperature (T/sub C/) and critical current density (J/sub C/), of PED-processed SmBCO films. The highest J/sub C/ value of 1.37 MA/cm/sup 2/ at 77 K in self field was obtained from an optimally processed sample using Ts of 900/spl deg/C (corresponding to real substrate temperature of 810/spl deg/C), PO/sub 2/ of 15 mTorr, and target-to-substrate distance of 9 cm, evidencing that this process is a potential alternative to the PLD process.

Intrinsic amorphous and microcrystalline silicon by hot-wire-deposition for thin film solar cell applications

The influence of various deposition parameters on the electrical and optical properties and the structure of amorphous and microcrystalline silicon films was investigated for material prepared by hot-wire (HW) CVD in a new multichamber deposition system, designed for the development of thin film solar cells. Prior to the material studies, careful measurement of the real substrate temperature under the influence of additional HW heating was performed. While good electronic quality and solar cell performance was found for a-Si:H layers, the μc-Si:H material showed very high spin densities, porosity and a characteristic structural inhomogeneity along the growth axis.

Feedback control of substrate temperature during the growth of near-lattice-matched InGaAs on InP using diffuse reflection spectroscopy

Diffuse reflection spectroscopy (DRS) is used to control substrate temperature to within ±2°C of user specified setpoint during the growth of near-lattice-matched InGaAs on InP. The same growth under constant thermocouple control would result in a 50°C rise in real substrate temperature. Feedback control is achieved using a nested proportional-integral-derivative (PID) control loop; the inner loop consists of a conventional Eurotherm-thermocouple feedback loop that controls the substrate heater power; the outer loop updates the thermocouple setpoint based on the difference between the user setpoint and the substrate (DRS) temperature using a PID control loop implemented in the control software. Frequency loop shaping, based on a dynamical model of the system obtained from an identification experiment, is used to tune the outer PID loop. In addition, the thermal disturbances that occur during effusion cell shutter operations must be rejected. In the simplest case, a single correcting step in the Eurotherm (thermocouple) setpoint is input when a shutter is toggled. Through disturbance identification and model inversion a more sophisticated disturbance rejection action from the controller can be obtained.

Closed-loop control of composition and temperature during the growth of InGaAs lattice matched to InP

Spectroscopic ellipsometry (SE) and diffuse reflection spectroscopy (DRS) are used to control the Ga mole fraction and substrate temperature, respectively, during the growth of InGaAs lattice matched to InP. Ga mole fraction is controlled to within ±0.002 of its target value and substrate temperature is controlled to within ±2 °C of its target value. The same growth under constant thermocouple control would result in a 50 °C rise in real substrate temperature and a Ga composition 1% above its target value. In both cases, feedback control is achieved using a nested proportional-integral-derivative (PID) control loop, where, the inner loop consists of the conventional Eurotherm-thermocouple feedback loop and the outer loop updates the thermocouple setpoint using a PID control loop implemented in the control software. For composition control, the Ga cell thermocouple setpoint is increased (decreased) 0.2 °C for every 0.002 that the Ga mole fraction, given by the SE sensor, deviates below (above) the target value. During substrate temperature control, the thermocouple setpoint is updated based on the temperature difference between the DRS sensor and the user setpoint. Frequency loop shaping, based on a dynamical model of the system obtained from an identification experiment, is used to tune the outer PID loop.

Exact determination of the real substrate temperature and film thickness in vacuum epitaxial growth systems by visible laser interferometry

A concise description of the application of laser interferometric thermometry (LIT) for exact calibration of the process manipulator thermocouple and, thus, for exact determination of the real substrate temperature in a MBE system is presented. A He-Ne laser visible 0.6328 μm light has been used as a probe, and a GaP plane-parallel wafer polished on both sides to an optical finish served as a calibration standard. The behaviour of the substrate temperature in dynamic thermal conditions has been tested experimentally with LIT and a long delay time has been found when the substrate temperature approaches an intended value at cooling or heating processes, after the heating block temperature of the manipulator has been changed. Finally, the experimental procedures of in situ determination of the growing film thicknesses with visible laser interferometry during MBE growth processes have been described for two cases, concerning films completely transparent to the laser light used and films only partly transparent to this light.

Accurate measurement of MBE substrate temperature

The behavior of real substrate temperature for radiatively heated MBE holders is measured using changes in the bandgap and refractive index with temperature. The infra-red spectroscopy techniques utilized are not sensitive to window coating and have no adjustable parameters. Using bandgap changes with temperature, we observed that the change in real substrate temperature is approximately 60% that of the indicated thermocouple change and that variations as large as 15°C occurred between “nominally identical” substrate holders. The real substrate temperature also changes by up to 10°C during growth and with opening and closing of high temperature doping furnaces.

In situ growth of high temperature superconductor thin films with evaporation techniques using an ozone jet

High-quality YBa/sub 2/Cu/sub 3/O/sub 7/ thin films were grown in situ on various substrates (SrTiO/sub 3/, Al/sub 2/O/sub 3/, and Si) using MBE (molecular beam epitaxy) techniques and an ozone jet. The yttrium and copper are evaporated from electron-gun sources and the barium is evaporated from a Knudsen cell. All sources are controlled by a single mass spectrometer feedback system to obtain the correct fluxes at high partial ozone pressures. During deposition, the partial ozone pressure at the substrate position is estimated to be 10/sup -3/ -10/sup -2/ mbar. The substrate holder temperature is 700 degrees C. The real substrate temperature is estimated to be lower than 650 degrees C. The films are analyzed with R(T), X-ray diffraction, and RBS (Rutherford backscattering) measurements. Scanning electron microscope photographs are taken of the surface. The best film so far is grown on SrTiO/sub 3/ and has a T/sub c.onset/ of 88 K and a T/sub c0/ of 80 K. One 200-nm-thick film grown on bare silicon has a T/sub c.onset/ of 88 K and a T/sub c0/ of 60 K. This film shows negligible superconductor-substrate interactions according to the RBS measurements.