Investigation of growth kinetics and incorporation of impurities in group III-nitrides and group III-dilute nitrides using mass spectroscopy

在国内和国际上，对氮化物半导体的商业和科学兴趣越来越高。III族氮化物（AlN、GaN和InN及其固溶体）越来越多地用于琥珀色、绿色、蓝色和白色发光二极管（LED），用于蓝色/UV激光二极管（LD）以及用于高功率、高频和高温电子器件。有两种常用的生长方法用于制备氮化物半导体-金属有机气相外延（MOVPE）和分子束外延（MBE）。在MBE中，氮主要作为氨或活性氮从等离子体源供应。尽管氮化物器件技术发展迅速，但等离子体辅助分子束外延（PA-MBE）和氨分子束外延（GS-MBE）的基本生长动力学在很大程度上是未知的，特别是对于非极性取向。这是因为观察到GaAs中的少量氮非常显著地减小了带隙，导致更长波长的发射。在这一领域，MBE是首选技术。尽管稀氮化物半导体的快速发展，基本的生长动力学在很大程度上是未知的，MBE生长完全基于经验知识。与此同时，在过去的十年中，自旋电子学已成为一个主要的研究课题，这需要磁性半导体。新兴的半导体自旋电子学领域为非易失性高速信息存储和处理提供了新的前景。在这一领域的一个重要里程碑是发现载流子介导的铁磁性GaAs掺杂锰。现在在诺丁汉，我们已经实现了世界纪录的铁磁转变温度，TC，在GaMnAs的173 K。然而，对于这些系统的广泛技术应用，需要显著高于300 K的TC。理论预测表明，对于空穴浓度大于3.5 × 10（20）cm-3的Ga_（1-x）Mn_xN（x > 0.05），居里温度应大于300 K。然而，铁磁半导体如GaMnN、GaCrN等的基本生长动力学在很大程度上也是未知的，并且再次完全基于经验知识。在飞利浦，以及最近在帝国理工学院和诺丁汉大学，开发了一种被称为调制束质谱（MBMS）的强大工具来研究MBE生长动力学。基本技术使用质谱仪来检测从生长膜中解吸的物质。吸附或解吸通量的调制允许区分质谱仪中来自真空室中的背景气体的信号和来自样品表面的信号。该方法结合反射高能电子衍射（RHEED）和俄歇电子能谱（AES）被用来开发MBE生长模型的GaAs使用的As 2和As 4。本计画的主要目的是利用调变射束质谱法（MBMS）发展详细的分子束外延成长模型，以探讨：a）氮在非极性及锌掺杂氮化镓中的掺入，B）氮在砷化镓基稀氮化物中的掺入，以及c）磁性杂质（锰、铬及铁）在纤锌矿及锌掺杂氮化镓中的掺入。

There is an increasingly high level of commercial and scientific interest in nitride semiconductors both nationally and internationally. The group III-nitrides (AlN, GaN and InN and their solid solutions) are being used increasingly for amber, green, blue and white light emitting diodes (LEDs), for blue/UV laser diodes (LDs) and for high-power, high-frequency and high temperature electronic devices. There are two common growth methods used to prepared nitride semiconductors - metal-organic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE). In MBE, nitrogen is mainly supplied either as ammonia or active nitrogen from a plasma source. Despite the rapid advances in nitride device technology, the basic growth kinetics are largely unknown for both plasma-assisted MBE (PA-MBE) and for ammonia MBE (GS-MBE), especially for non-polar orientations.There is also an increasing level of commercial and scientific interest in dilute nitride semiconductors both nationally and internationally for long-wavelength optical communications. This stems from the observation that small quantities of nitrogen in GaAs reduce very significantly the band gap leading to longer wavelength emission. In this field, MBE is the preferred technology. Despite the rapid advances in dilute nitride semiconductors, the basic growth kinetics are largely unknown and MBE growth is based entirely on empirical knowledge. At the same time, during the last decade spintronics has become as a major subject of research, which requires magnetic semiconductors. The emerging field of semiconductor spintronics offers new prospects for non-volatile high speed information storage and processing. An important milestone in this field was the discovery of carrier-mediated ferromagnetism in GaAs doped with Mn. Now at Nottingham we have achieved a world record ferromagnetic transition temperatures, TC, in GaMnAs of 173K. However, for widespread technological use of these systems, a TC significantly above 300K is needed. Theoretical predictions suggest that for Ga1-xMnxN (x > 0.05) having a hole concentration of >3.5x10(20)cm-3 the Curie temperature should be >300K. However, the basic growth kinetics for ferromagnetic semiconductors such as GaMnN, GaCrN etc. is also largely unknown and again based entirely on empirical knowledge.At Philips, and more recently at Imperial College and University of Nottingham, a powerful tool was developed to study the MBE growth kinetics known as modulated beam mass spectrometry (MBMS). The basic technique uses a mass spectrometer to detect the species desorbing from the growing film. Modulation of the adsorbed or desorbed fluxes allows one to distinguish between signals in the mass spectrometer coming from background gases in the vacuum chamber and those coming from the sample surface. This method in combination with reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES) was used to develop the MBE growth models for GaAs using As2 and As4. The main aim of this project is to use the modulated beam mass spectrometry (MBMS) method to develop detailed MBE growth models for: a) nitrogen incorporation in non-polar and zinc-blende GaN, b) nitrogen incorporation in GaAs based dilute nitrides and c) incorporation of magnetic impurities (Mn, Cr and Fe) into wurtzite and zinc-blende GaN.