8.1 INTRODUCTION

GaAs is one of the most important compound semiconductor materials because it is used not only for infrared LDs and infrared and red LEDs1 but also used for high frequency electronic devices2 which competes with Si in high frequency and low power operations as described in Chapter 6. The applications of variously doped GaAs are summarized in Table 8.1. The consumption of GaAs substrates is increasing year by year for these optoelectronic and electronic devices3 and now exceeds about three hundred million dollars per year.

Industrially, conductive GaAs is produced mainly by the HB and HGF methods and semi-insulating GaAs is produced mainly by the LEC method. Production by the VB/VGF methods is however increasing because higher quality crystals can be grown.

Because of the importance of GaAs and because of the interesting physical properties, GaAs is the compound semiconductor material of all compound semiconductors about which the largest number of studies among various compound semiconductors has been performed so far. There are various reviews on GaAs. ^{4 9}

8.2 PHYSICAL PROPERTIES

The details of the physical properties of GaAs can be found in the literature.10 The main properties are summarized in Table 8.2. As seen from the table, GaAs has a lattice constant with which that of AlGaAs mixed crystal...