Due to its outstanding material properties, 4H-SiC is well-suited for the production of energy efficient power electronics. Power electronic devices such as bipolar diodes with a high blocking voltage require thick n-type 4H-SiC epilayers with a high minority carrier lifetime [1] and low defect density especially basal plane dislocation (BPD) density. For high quality epilayers, the growth rate is limited to 30 µm/h for the conventional epitaxial process on 4° off-cut substrates. In the transport limited regime, an increase of the growth rate is only possible by increasing the silane partial pressure. However, if Si species supersaturate normal step-flow growth is inhibited and polycrystalline growth is observed. However, by adding hydrogen chloride (HCl) to the process, step-flow growth can be conserved even at growth rates up to 100 µm/h, therefore, making thick epilayers economically feasible [2]. It has been reported [3] that the addition of HCl reduces the concentration of certain point defects which act as recombination centers and hence, increases the minority carrier lifetime. Furthermore, the surface morphology and defects could be optimized by HCl assisted growth [4]. Most of these studies have been performed on 8° and 0° off-cut substrates.

In recent years we optimized extensively our growth process on 4° off-cut substrates with respect to BPD density and suitability of the thick epilayers for production of bipolar devices [5]. This paper investigates the benefits of HCl assisted growth with respect growth rate, surface morphology and minority carrier lifetime.

Therefore, homoepitaxial 4H-SiC epilayer were grown by chemical vapour deposition (CVD) in a horizontal hot wall reactor (Epigress VP508GFR). The epilayers were grown on the (0001) Si-face on substrates with a 4° off-cut towards the <11-20> direction. HCl is added to the conventional CVD growth process of 4H-SiC where silane and propane act as precursors and hydrogen as carrier gas.

The process conditions are described by the Cl/Si, Si/H and C/Si ratios while keeping the growth temperature, reactor pressure and total flow constant. Nominally undoped epilayers as well as nitrogen doped n-type epilayers with a donor concentration of 1×10¹⁵ cm^-3 were grown. 

The Cl/Si, Si/H and C/Si ratio of the HCl assisted growth was varied systematically on 4° off-cut substrates in order to investigate the surface morphology, BPD density, reduce deep level defects and increase the minority carrier lifetime. Epilayers grown by the conventional process and HCl assisted growth will be compared and tested for their suitability for bipolar devices.

This work was part of the SiC-WinS project funded by the Bavarian Research Foundation (BFS) under contract number AZ-1028-12.

References:

[1] J. Cooper et al.: Proceeding of the IEEE 90 (2002) 0018-9219

[2] H. Pedersen et al.: Chemical Reviews 112 (2012) 2434-2453

[3] L. Calcagno et al.: Journal of Applied Physics 102 (2007) 043523

[4] J. Zhang et al.: Material Science Forum 600-603 (2009) 103-106

[5] B. Kallinger et al.: Journal of Crystal Growth 314 (2011) 21-29

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/29006 must be provided.

1. Formation of dislocations in highly doped n-type Czochralski silicon
2. Behaviour of Particle Depots in Molten Silicon Under Terrestrial And Microgravity Conditions
3. Evaluation of different baffle geometries in an ammonothermal system by a local numerical 3D model
4. Influencing the crystallization behaviour of multi crystalline silicon in a R&D furnace
5. Interaction of Foreign phase particles with moving solid-liquid interface during directional solidification of silicon for photovoltaics
6. Low dislocation density GaN-templates grown by the Low Pressure Solution Growth technique