Beyond modulation doping

超越调制掺杂

• 批准号: EP/J003417/1
• 负责人: David Ritchie
• 金额: $ 109.4万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FJ003417%2F1
• 关键词: Beyond; modulation; doping

When an impurity atom in a semiconductor crystal has more (or fewer) valence electrons than the atom it replaces, it can donate one or more electrons to (or accept them from) the crystal lattice. The deliberate addition of such impurities, called dopants, is the traditional means of generating mobile charge carriers (negatively-charged electrons or positively-charged holes) within semiconductor devices, including the silicon-based metal-oxide-semiconductor field-effect transistors (MOSFETs) and compound semiconductor high-electron-mobility transistors (HEMTs) ubiquitous in modern electronics.High-mobility, gallium-arsenide-based HEMTs in particular, which can be made from ultrahigh-purity wafers grown by molecular beam epitaxy (MBE), have also been instrumental in the discoveries of new physics, including the fractional quantum Hall (FQH) effect, microwave-induced resistance oscillations, Wigner solid phases in magnetic field, ballistic transport and conductance quantisation in one-dimensional channels, single-electron quantum dots, Kondo physics, spin-based solid-state qubits, possible excitonic superfluidity in double-quantum-well structures, and possible non-Abelian statistics in certain novel FQH states.Even with the technique of modulation doping, where dopants are placed far away from the conducting channel, disorder due to the ionised dopants can still be felt by the carriers in a high-purity wafer, and this disorder can interfere with phenomena being studied. However, these intentional dopants are not necessary if one uses instead an external electric field to electrostatically induce a two-dimensional electron gas (2DEG) or hole gas (2DHG) at the semiconductor heterointerface. This electric field can be applied with electrostatic gates on the front and/or back side of devices. Although the proof-of-principle demonstration of undoped devices (which required only one working device) was reported more than eighteen years ago by Bell Labs (USA), the complex cleanroom fabrication process and the ensuing very low yield of working devices have prevented the use of undoped devices from becoming mainstream. Over the last three years, our group has made a number of technological breakthroughs which allow a 90+% yield of working devices, including Hall bars and nanostructures (e.g., quantum dots). This yield is now high enough to have research projects depend on a steady, reliable supply of high-quality samples.To capitalise on this success, we propose to combine our ability to fabricate such devices on demand with our expertise in MBE semiconductor wafer growth and millikelvin temperature measurements to further progress on two of the topics listed above, the fractional quantum hall effect and spin-based solid-state qubits. Many "exotic" FQH states present in the second Landau level do not fit the Laughlin/Jain theory which describes "conventional" FQH states, and are particularly sensitive to dopant-induced disorder. Our experimental programme will shed light on the nature of these states, particularly the famous state at filling factor 5/2 and its possible non-Abelian properties. Gate-defined electron spin qubits in GaAs were once amongst the forerunner systems for the realisation of a quantum computer. However, this system suffers from the presence of hyperfine interactions and charge noise, both of which cause spin decoherence on timescales too short for a practical quantum computer. Our experimental programme will demonstrate how both hyperfine interactions and charge noise are significantly reduced when gate-defined double quantum dots are fabricated from undoped 2DHGs.Our proposed work will yield fundamental insights into physical phenomena not easily accessible using even the highest quality doped heterostructures.

当半导体晶体中的杂质原子比它所取代的原子具有更多（或更少）的价电子时，它可以向晶格提供一个或多个电子（或从晶格接受电子）。故意添加此类杂质（称为掺杂剂）是在半导体器件中产生移动电荷载流子（带负电的电子或带正电的空穴）的传统方法，包括现代普遍存在的硅基金属氧化物半导体场效应晶体管（MOSFET）和化合物半导体高电子迁移率晶体管（HEMT） 尤其是高迁移率砷化镓基 HEMT，它可以由通过分子束外延 (MBE) 生长的超高纯度晶圆制成，在新物理学的发现中也发挥了重要作用，包括分数量子霍尔 (FQH) 效应、微波引起的电阻振荡、磁场中的维格纳固相、弹道输运和电导量子化。 一维通道、单电子量子点、近藤物理、基于自旋的固态量子位、双量子阱结构中可能的激子超流性以及某些新颖的 FQH 态中可能的非阿贝尔统计。即使采用调制掺杂技术，其中掺杂剂放置在远离导电通道的位置，由于电离掺杂剂造成的无序仍然可以被载流子感受到 高纯度晶圆，这种无序会干扰正在研究的现象。然而，如果使用外部电场在半导体异质界面处静电感应二维电子气 (2DEG) 或空穴气 (2DHG)，则不需要这些有意的掺杂剂。该电场可以通过器件正面和/或背面的静电门施加。尽管美国贝尔实验室在十八多年前就报道了未掺杂器件（仅需要一个工作器件）的原理验证演示，但复杂的洁净室制造工艺以及随之而来的工作器件的极低产量阻碍了未掺杂器件的使用成为主流。在过去的三年里，我们的团队取得了多项技术突破，使包括霍尔条和纳米结构（例如量子点）在内的工作器件的成品率达到 90% 以上。现在的产量已经足够高，足以使研究项目依赖于稳定、可靠的高质量样品供应。为了利用这一成功，我们建议将我们按需制造此类设备的能力与我们在 MBE 半导体晶圆生长和毫开尔文温度测量方面的专业知识相结合，以进一步在上面列出的两个主题上取得进展，即分数量子霍尔效应和基于自旋的固态量子位。第二朗道能级中存在的许多“奇异”FQH 状态不符合描述“传统”FQH 状态的 Laughlin/Jain 理论，并且对掺杂剂引起的紊乱特别敏感。我们的实验程序将揭示这些状态的性质，特别是填充因子 5/2 的著名状态及其可能的非阿贝尔性质。 GaAs 中的门定义电子自旋量子位曾经是实现量子计算机的先驱系统之一。然而，该系统存在超精细相互作用和电荷噪声，这两者都会导致自旋退相干的时间尺度对于实用的量子计算机来说太短。我们的实验计划将展示当由未掺杂的 2DHG 制造门定义的双量子点时，超精细相互作用和电荷噪声如何显着降低。我们提出的工作将对物理现象产生基本的见解，即使使用最高质量的掺杂异质结构也不容易获得这些物理现象。

项目成果

Non-invasive charge detection in surface-acoustic-wave-defined dynamic quantum dots

表面声波定义的动态量子点中的非侵入式电荷检测

• DOI: 10.1063/1.4966667
• 发表时间: 2016
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Astley M

Determining energy relaxation length scales in two-dimensional electron gases

确定二维电子气中的能量弛豫长度尺度

• DOI: 10.1063/1.4926338
• 发表时间: 2015
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Billiald J

Thermal dissociation of free and acceptor-bound positive trions from magnetophotoluminescence studies of high quality GaAs / Al x Ga 1 - x As quantum wells

高质量 GaAs / Al x Ga 1 - x As 量子阱的磁光致发光研究中游离和受主结合的正三重子的热解离

• DOI: 10.1103/physrevb.93.165303
• 发表时间: 2016
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Bryja L

Growth variations and scattering mechanisms in metamorphic In0.75Ga0.25As/In0.75 Al0.25As quantum wells grown by molecular beam epitaxy

分子束外延生长变质In0.75Ga0.25As/In0.75 Al0.25As量子阱的生长变化和散射机制

• DOI: 10.1016/j.jcrysgro.2015.02.038
• 发表时间: 2015
• 期刊: Journal of Crystal Growth
• 影响因子: 1.8
• 作者: Chen C

Quantized escape and formation of edge channels at high Landau levels and edge transport mediated zero-differential resistance states

高朗道水平下的量子逃逸和边缘通道的形成以及边缘传输介导的零微分电阻状态

• DOI: 10.1103/physrevb.90.045301
• 发表时间: 2014
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Chepelianskii A