A. Boyer

Elaboration of Bi2Te3 by metal organic chemical vapor deposition

Abstract Bi2Te3 layers were elaborated for the first time using metal organic chemical vapor deposition. The films composition is stoichiometric when the following conditions are verified: substrate temperature lower than 500 °C, VI/V ratio greater than 3, TMBi partial pressure lower than 2 × 10−4 atm. By X-ray diffraction and MEB observation, we noticed the polycrystalline structure of the layers. The high thermoelectric power (+ 190 V K−1 for the n-type layer and −94 V K−1 for the n-type layer) of this material is promising for device applications.

MOCVD growth of Bi2Te3 layers using diethyltellurium as a precursor

Abstract The growth of Bi 2 Te 3 thin films by metal organic chemical vapour deposition (MOCVD) using diethytellurium and trimethylbismuth as tellurium and bismuth sources respectively is investigated on pyrex substrates. The results of growth rate, morphology, electrical and thermoelectrical properties as a function of growth parameters are given. The prepared films were always n -type. Film properties, such as electrical resistivity, mobility, carrier concentration, thermoelectric power and X-ray diffraction were studied at 300 K. For VI/V ratio greater than 6, we found an electrical resistivity lower than 9 μ Ω.m and a thermoelectrical power equal to 210 μ V/K. Hall mobility varies from 28 and 150 cm 2 /V.s. These initial results suggest a significant potential of MOCVD growth for large-scale production of thermoelectric material.

Optimal crystal growth conditions of thin films of Bi2Te3 semiconductors

Abstract Crystal growth conditions of Bi 2 Te 3 narrow bandgap semiconductors have been studied using molecular beam epitaxy method. It was applied to the growth of Bi 2 Te 3 on Bridgman single-crystal substrate Sb 2 Te 3 . Substrate ingots were taken from the natural cleavage along the (0001) plane. The deposited conditions have been studied as a function of substrate temperature ( T s ) and flux ratio ( F R = F(Te)/F(Bi)). The quality of deposited layers was controlled by X-ray diffraction, scanning electron microscope (SEM), secondary ion mass spectroscopy (SIMS) depth profiling and energy-dispersive X-ray (EDX) microanalyser. The sticking coefficients K s (Te) and K s (Bi) of the elements that compose Bi 2 Te 3 were determined. It was found that the stoichiometry of deposited layers depended on substrate temperature and flux ratio. It was observed that all deposited layers were single-crystal in the orientation of their substrates with a small shift due to the stress in layer.

Growth of (Bil−xSbx)2Te3 thin films by metal-organic chemical vapour deposition

Abstract The effects of VI/V ratio on electrical and thermoelectrical properties of p-type (Bi 1− x Sb x ) 2 Te 3 elaborated by metal-organic chemical vapour deposition (MOCVD) in horizontal quartz reactor are discussed. The deposited layers exhibit a polycrystalline structure and an improvement in the intensity is observed with increasing the VI/V ratio. The quality of the layers is measured by means of the Energy dispersive X-ray (EDX) microanalyser and scanning electron microscopy (SEM). It is observed that the layers are stoichiometric when the VI/V ratio exceeds 3 and the surface texture is improved with increasing this ratio. The electrical properties of the thin films dependent on the VI/V ratio. The measurements of the Seebeck coefficient suggest a significant potential of MOCVD growth for large-scale production of thermoelectric materials.

Fast humidity sensor using optoelectronic detection on pulsed Peltier device

Abstract In order to develop a new way to use a Peltier device in a fast humidity sensor, we have studied the optical signal of a photodetector when water condensation appears on the cold side of a commercial Peltier module. The thermoelectric device is used at pulsed rate. During the cooling the applied current is stopped as soon as a variation of the optical response, due to the appearance of water droplets, is observed. A reverse pulse is then applied to return quickly to the ambient temperature. We have measured the response time of a small commercial Peltier module. The experimental thermal time constant τth measured during the cooling using a thermocouple is typically τth = 3.6 s. A calculated estimation of the reverse pulse time is given in order to optimize the return to the equilibrium room temperature for low relative humidity. The last part of this work is devoted to measurements of the relative humidity HR. The delay time TC of the optical detection is plotted as a function of humidity level. TC is function of the Peltier current supply Ipeltier: with Ipeltier equal to 700 mA, we have observed a delay time TC in the range 0.25 s ≤ TC ≤ 12.2 s for 15% ≤ HR ≤ 70%.

Structural, electrical and thermoelectrical properties of (Bi1 − xSbx)2Te3 thin films grown by MOCVD process

Abstract The electrical and thermoelectrical performance of p-type (Bi 1 − x Sb x ) 2 Te 3 obtained by metal organic chemical vapour deposition (MOCVD) in a horizontal quartz reactor on pyrex substrate are discussed. The quality of the deposited layers was checked by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Hall effect and resistivity measurements were performed. It was found that the electrical properties of (Bi 1 − x Sb x ) 2 Te 3 thin films depend strongly on the growth parameters. The measurement of the Seebeck coefficient (S = 235μV/K) lead us to confirm the significant potential of the MOCVD method to produce a material with a good potential for thermoelectric applications.