Materials Science and Engineering B51 (1998) 202 – 206 Mobility (10 6 cm 2 V - 1 s - 1 ) of 2DEGs, 30 nm from ex situ patterned GaAs regrowth interfaces T.M. Burke a , D.A. Ritchie a , E.H. Linfield a , M.P. O’Sullivan a , J.H. Burroughes b, *, M.L. Leadbeater b , S.N. Holmes b , C.E. Norman b , A.J. Shields b , M. Pepper ab a Caendish Laboratory, Uniersity of Cambridge, Madingley Road, Cambridge CB30HE, UK b Toshiba Cambridge Research Centre, 260 Cambridge Science Park, Milton Road, Cambridge CB44WE, UK Abstract We have regrown, on ex situ patterned GaAs substrates, using hydrogen radical decontamination, two-dimensional electron gases (2DEGs) confined in 15 nm quantum wells (QWs) with the inverted AlGaAs/GaAs interface 30 nm from the regrowth interface (RI), which conduct before illumination at 1.5 K. Mobilities in excess of 1 ×10 6 cm 2 V -1 s -1 have been achieved. We have not observed a degradation in the mobility for a constant carrier concentration between 2DEGs, 200 and 30 nm from the RI. A control structure with the 2DEG 30 nm from the RI was also grown on an un-patterned GaAs substrate that was only thermally cleaned, which had a maximum mobility of 3 ×10 4 cm 2 V -1 s -1 after illumination at 1.5 K. © 1998 Elsevier Science S.A. All rights reserved. Keywords: Regrowth; 2DEG; Hydrogen decontamination 1. Introduction Regrowth over ex situ patterned substrates is a wafer scale technology that potentially allows the length scales achievable by MBE or MOCVD growth to be exploited to fabricate quantum semiconductor struc- tures with two- or three-dimensional confinement. We have shown by fabricating various prototype structures that novel one- [1] and zero-dimensional [2] structures are possible. To exploit the full potential of the tech- nique, high purity and ordered regrowth interfaces are required to grow the active regions very close to the regrowth interface (RI) and hence fabricate highly- confined structures. Hydrogen radical and ion exposure have been shown to remove contaminants such as oxygen and hydrocarbons from GaAs surfaces at rela- tively low temperatures [3 – 13]. Recently, there have been reports showing that these contaminants may be removed to below the secondary ion mass spectrometer (SIMS) detection limits [9,11]. It has also been shown that the surface after hydrogen radical exposure is much smoother than after thermal treatments and that photoluminescence (PL) efficiency and peak width are much improved [10]. Kondo has also shown that nar- row spacer layer 2DEG structures may be grown within 20 nm of a growth interface that show negligible perfor- mance deterioration compared with 2DEGs grown 600 nm away, at 77 K [14]. There have also been several device structures fabricated [15 – 17] that make use of the hydrogen decontamination process. For example, the surface tunnel transistors (STT) fabricated by Ue- mura et al. [17–19]. In this paper, we present our results on reducing the distance between high mobility two-dimensional elec- tron gases (2DEGs) and the RI. The mobilities ob- tained were in excess of 1 ×10 6 cm 2 V -1 s -1 at 1.5 K for 2DEGs between 30 and 50 nm from the RI. The wafers are ex situ patterned and then exposed to a hydrogen radical beam in a UHV chamber attached by UHV transfer chambers to a MBE reactor. We have used the 2DEG as a measure of the regrowth quality because the mobility is much more sensitive to contam- ination levels in the 2DEG region than other diagnostic techniques such as SIMS [20]. Although the 2DEG proximity work encompassed a large number of re- growths with the 2DEG to RI distance varied from 200 to 30 nm, only the last four samples in close proximity to the RI will be discussed. We will also present some * Corresponding author. 0921-5107/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S09 21- 5 1 07(97)00 2 60 -2