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

国内外对氮化半导体的商业和科学兴趣日益高涨。iii族氮化物（AlN， GaN和InN及其固溶体）正越来越多地用于琥珀色，绿色，蓝色和白色发光二极管（led），蓝色/紫外激光二极管（ld）以及大功率，高频和高温电子设备。制备氮化半导体有两种常用的生长方法：金属有机气相外延（MOVPE）和分子束外延（MBE）。在MBE中，氮主要以氨或来自等离子体源的活性氮的形式提供。尽管氮化物器件技术发展迅速，但等离子辅助MBE （PA-MBE）和氨MBE （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。在国内和国际上，对用于长波光通信的稀氮化半导体的商业和科学兴趣也越来越大。这源于观察到砷化镓中少量的氮会显著降低带隙，从而导致更长的波长发射。在这一领域，MBE是首选技术。尽管稀氮半导体的发展迅速，但基本的生长动力学在很大程度上是未知的，MBE的生长完全基于经验知识。同时，近十年来，自旋电子学已成为一个重要的研究课题，这需要磁性半导体。半导体自旋电子学这一新兴领域为非易失性高速信息存储和处理提供了新的前景。该领域的一个重要里程碑是在掺杂锰的砷化镓中发现了载流子介导的铁磁性。现在在诺丁汉，我们已经达到了世界纪录的铁磁转变温度，TC，在173K的gamna中。然而，对于这些系统的广泛技术使用，需要显著高于300K的TC。理论预测表明，对于空穴浓度为>3.5x10(20)cm-3的Ga1-xMnxN (x > 0.05)，其居里温度应为>300K。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，开发了一种强大的工具来研究MBE生长动力学，称为调制束质谱（MBMS）。基本技术是使用质谱仪来检测从生长膜中脱吸的物质。对吸附或解吸通量的调制使人们能够区分质谱仪中来自真空室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）建立了以As2和As4为原料的GaAs的MBE生长模型。该项目的主要目的是使用调制束质谱（MBMS）方法开发详细的MBE生长模型：a)非极性和锌-闪锌矿GaN中的氮掺入，b) GaAs基稀氮化物中的氮掺入，以及c)纤锌矿和锌-闪锌矿GaN中磁性杂质（Mn， Cr和Fe）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.