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

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.