4H-SiC: a material for high temperature Hall sensor Jean-Louis Robert a,* , Sylvie Contreras a , Jean Camassel a , Julien Pernot a , Eric Neyret a,b , Le Âa Di Cioccio b , Thierry Billon b a Groupe d'Etude des Semiconducteurs, UM2-CNRS (UMR 5650), CC074, 34095 Montpellier Cedex 5, France b CEA/LETI, 17 rue des Martyrs, 38054 Grenoble Cedex 9, France Received 12 June 2001; received in revised form 14 August 2001; accepted 10 September 2001 Abstract In this work, we show that progress made in the crystal growth and device processing technology of 4H-SiC open the way to the development of Hall sensors presenting a low thermal drift with a large sensitivity (930 V/(AT)) in a wide temperature range. Above 300 K, low doped 4H-SiC epilayers areworking in the exhaustion regime. Transport measurements show a constant value of the carrier density from 300 to 800 K. Simultaneously, the resistivity increases linearly at a rate of 3400 ppm/K between 500 and 800 K leading to the possibility to use the same samples as temperature sensor. # 2002 Elsevier Science B.V. All rights reserved. Keywords: 4H-SiC; Hall sensor; Exhaustion regime; High temperature 1. Introduction SiC crystallizes in different forms usually termed poly- types. A stacking of bilayer Si±C along the crystal growth axis composes silicon carbide. The order and periodicity of the bilayer stacking de®ne the polytype of the crystal. With this respect, SiC is a family name which represents a class of morethan150differentsemiconductormaterials.Only,afew of these polytypes have application ®elds and at the present time, only 4H-SiC (for electronics), 6H-SiC (as conducting substrate for nitride-based opto-electronics) and 3C-SiC (for high temperature sensor development) are under con- sideration for industrial applications. Due to its wide band gap (3.26 eV), high thermal con- ductivity (3±5 W/(cm K)) and high saturation velocity (2:2 10 7 cm/s), 4H-SiC appears to be one of the best suited semiconductor for high temperature, high power and high frequency electronic devices. The last several years, SiC semiconductor technology made tremendous progress in reason of the availability of large diameter substrates of hexagonal (4H and 6H) polytypes [1]. Considering their shallow impurity levels and its high mobility [2], 4H-SiC is the evident polytype for electronic application. In this work, we investigate this polytype for Hall sensor working at high temperature. In the forthcoming years, this should challenge the common silicon devices [3]. A Hall sensor must have a linear response versus bias current I and perpendicular magnetic ®eld B through the Hall voltage V H , as V H  K H IB (1) where K H  R H d  r H qnd (2) where q is the electron charge and R H the Hall coef®cient. In the ideal case, r H the Hall scattering factor, n the free electron density and d the thickness of the active layer must be independent of temperature T . We will show that 4H-SiC properties ful®ll these requirements at high temperature. Our paper is organized as follows. First, we present the device structure. Second, we discuss the doping level needed to reach the exhaustion regime from room temperature. We describe the electrical properties of such low doped layer and evidence the scattering mode which control the tem- perature dependence of the Hall factor. Third, we exhibit performances of our demonstrator: large sensitivity and low thermal drift between 300 and 800 K. We propose a possi- bility to use the same device to perform a temperature sensor with a great sensitivity. 2. Device fabrication and experiment It is well-known that CVD is the best technique to deposit high quality layers in the case of SiC [4]. A home made Sensors and Actuators A 97±98 (2002) 27±32 * Corresponding author. Tel.: 33-46714-3794; fax: 33-46714-3760. E-mail address: robert@ges.univ-montp2.fr (J.-L. Robert). 0924-4247/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0924-4247(01)00812-3