Fabrication of one-dimensional GaAs channel-coupled InAs quantum dot memory device by selective-area metal-organic vapor phase epitaxy

Abstract

Narrow wirelike openings were defined on SiO 2 -masked GaAs ͑001͒ substrates by electron-beam lithography and wet chemical etching methods. A one-dimensional GaAs channel-coupled InAs quantum dot memory device was fabricated in this opened area by the selective-area metal-organic vapor phase epitaxy. Drain current measurement by sweeping the gate voltage forward and backward showed clear hysteresis up to 180 K due to electrons charging into the quantum dots with a threshold voltage difference ͑⌬V th ͒ of 165 mV at 20 K and 29 mV at 180 K. Comparison of experimental ⌬V th values with the theoretically calculated ones showed that around 300 and 50 electrons were responsible for the memory operation at 20 and 180 K, respectively. Real time measurements showed that the write/erase states of the memory device were discriminated for more than 5 min at 20 K and about 100 s at 77 K. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.2120905͔There has been growing interest in quantum dot information storage devices using quantum dots ͑QDs͒ as storage media. The operation of a quantum dot memory ͑QDM͒ device depends on the discrete emission and capture of electrons, and not on the average behavior of hundreds of thousands of electrons, as is the case in today's flash memory devices. In general, the QDM devices mainly consist of a quantum dot layer to store electrons and a channel in close vicinity to sense them. [1][2][3][4][5] The storing and releasing of electrons into and from the QD energy levels is solely determined by the voltage of a control gate. While many studies of silicon QDM devices have addressed various key features, such as fabrication, room-temperature operation, the single electron charging effect, etc., 1,2 only a few have addressed InAs QDM devices and most of them comprising several hundreds or thousands of QDs. [3][4][5] Since storing information in an economic way requires high packaging density and low power consumption, the number of QDs must be reduced, and, consequently, the sensing channel should also be sufficiently reduced to enable sensing of a small potential change in the QDs caused by charging and discharging effects. Selective-area metalorganic vapor phase epitaxy ͑SA-MOVPE͒ growth is a key technology in fabricating various kinds of semiconductor nanostructures and their integrated circuits in high density. 6 We have, therefore, attempted to fabricate an InAs QDM device using SA-MOVPE. The self-limited growth mechanism associated with SA-MOVPE grown GaAs wires on masked GaAs ͑001͒ substrates naturally reduces the top width. 6,7 We utilized this natural width reduction mechanism to define narrow channels and then grew a few InAs QDs on the top to complete a memory structure requiring few electrons to operate.We first defined a narrow wirelike opening with a length of 4 m in the ͓−110͔ direction and a width of 600 nm in the ͓110͔ direction on SiO 2 -masked GaAs ͑001͒ substrates by electron-beam lithography and wet chemical etching. Using a low-pressure MOVPE system operating at 76 Torr,...

Carrier storage time of milliseconds at room temperature in self-organized quantum dots

“…Wie im vorangegangenen Abschnitt ausgeführt, weisen DRAM und Flash unterschiedliche Vor-und Nachteile bezüglich ihrer Kenndaten auf. Eine Gegenüberstellung der wichtigsten Kenngrößen gibt Tabelle 2.1 9 . Die Vorteile eines Speichertyps sind mit grüner Schrift, die Nachteile mit roter Schrift angegeben.…”

“…Prinzipiell können drei Typen von Banddiskontinuitäten an Heterogrenzflächen auftreten 9 (siehe Abb. 3.1): 9 [28]: E. T. Yu et al, Solid State Phys. 46, 1 (1992).…”

“…Vielmehr wurden Ladungsträgerrelaxationszeiten im Bereich von Pikosekunden gemessen. 8,9 Verschiedene Relaxationsprozesse bandübergänge in selbstorganisierten InGaAs/GaAs-Quantenpunkten. Für eine Quantisierungsenergie von 24 meV wurde eine Relaxationszeit für Löcher von 0, 6 ps bestimmt.…”

Time‐resolved detection of many‐particle hole states in InAs/GaAs quantum dots using a two‐dimensional hole gas up to 77 K

“…Furthermore, QDs are very promising for memory units with nano-scale feature sizes. The feasibility of such a QD-based Flash memory has been demonstrated recently [6,7]. In this paper, we study the coupling between self-organized InAs/GaAs QDs and an adjacent two-dimensional hole gas (2DHG) at temperatures ranging from 4 K to 100 K. Capacitance-voltage (C-V) measurements and time-resolved measurements of the source-drain current in the 2DHG reveal the discrete electronic structure of the InAs/GaAs QDs and give access to the many-particle hole states of the QD ensemble.…”

3 ns single-shot read-out in a quantum dot-based memory structure

“…[2][3][4][5][6][7] The QDs are used as storage nodes that are embedded into a modulation-doped field-effect (MODFET) structure which is used to perform the write, erase, and read operations. 6 The QDs offer large confinement potentials which could facilitate long storage times up to non-volatility (more than ten years).…”