%0 Journal Article
%T Room-Temperature Hysteresis in a Hole-Based Quantum Dot Memory Structure
%A Tobias Nowozin
%A Michael Narodovitch
%A Leo Bonato
%A Dieter Bimberg
%A Mohammed N. Ajour
%A Khaled Daqrouq
%A Abdullah Balamash
%J Journal of Nanotechnology
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/797964
%X We demonstrate a memory effect in self-assembled InAs/Al0.9Ga0.1As quantum dots (QDs) near room temperature. The QD layer is embedded into a modulation-doped field-effect transistor (MODFET) which allows to charge and discharge the QDs and read out the logic state of the QDs. The hole storage times in the QDs decrease from seconds at 200£¿K down to milliseconds at room temperature. 1. Introduction Today¡¯s semiconductor memory market is divided mainly between two memories: the dynamic random access memory (DRAM) and the flash, both having their advantages and disadvantages [1]. The DRAM is fast but volatile, while the flash is nonvolatile but suffers from a slow write time. The semiconductor memory community hence looks for alternatives to combine the advantages of both memories in what is termed the ultimate memory [2]. A promising option which could facilitate nonvolatility with fast write times is a memory based on self-organized quantum dots (QDs) [3]. The concept uses the confining properties of QDs to store data and a modulation-doped field-effect transistor (MODFET) to perform the necessary memory operations (write, erase, and read) [4, 5]. One key advantage is a wide variety of different materials when using III-V compound semiconductors, hence allowing to specifically tailor the band structure and tune the storage time according to the needs. The other key advantage is a very fast carrier capture time in QDs, which is in the range of some picoseconds at room temperature [6, 7]. Write times of a few nanoseconds in QDs have already been demonstrated, yet limited by the parasitics of the device [8]. Full memory operation has been demonstrated by various groups, yet the memory operation was either limited to low temperatures [9¨C11] or the storage of charges in the QDs was questioned and attributed to defects [12]. In this paper, we present a QD memory based on InAs QDs embedded into a MODFET (GaAs/ As) which can operate at much higher temperatures than hitherto. Hysteresis measurements prove a memory effect up to room temperature. 2. Sample The sample investigated here has been grown by molecular beam epitaxy (MBE). A schematic of the structure is shown in Figure 1. On top of a semi-insulating substrate, a 1000-nm-wide buffer layer of nominally undoped As is grown. Then, a -doped As layer with £¿ and 30£¿nm width is deposited, which serves as a doping layer to provide holes for the channel. After a 7-nm-wide As spacer layer, an 8-nm-wide GaAs layer is grown to form the channel, in which a two-dimensional hole gas (2DHG) forms. Another 28£¿nm of undoped
%U http://www.hindawi.com/journals/jnt/2013/797964/