Lattice-Matching Growth of InGaAIN Systems
- PDF / 615,530 Bytes
- 12 Pages / 414.72 x 648 pts Page_size
- 90 Downloads / 192 Views
crystal of[8]. InNThis has success been successively grown under control high flow rate ratios group V group has HI sources has made composition possible. Theofquality oftoInGaN improved at a growth temperature of 800°C such that photoluminescence has been observed. At present, using the growth methods mentioned above, an InGaN/AIGaN double-heterostructure (DH structure) has been fabricated and a candela-class DH light-emitting-diode (LED) has been obtained [9]. Optically pumped stimulated emission from a GaN/AIGaN DH structure has also been demonstrated [10]. However, no laser diode (LD) with an InGaAIN system exists which oscillates with current injection. Present demand requires an LD with an InGaAIN system to be fabricated. To achieve this, much higher quality material through lattice-matching growth on a substrate needs to be attained. Of course, the lattice matching between respective layers of configuring devices is also important. This has not been as large a problem in the device lifetimes of InGaA1N LEDs up to now, however, the strain due to lattice-mismatch may decrease lifetime in devices such as ZnSe-based blue-green LDs and LEDs. Lattice-matching growth has been a basic technique of epitaxial growth throughout its history. In this paper, lattice-matching growth is reviewed. The substrate materials suitable for complete and near lattice-matching growth are described. The control of composition of InGaN which is important for light emitting devices and lattice-matching growth is also shown. SUBSTRATE FOR InGaA1N SYSTEM .Therelationship between the lattice constant and band-gap energy is a basic consideration in device fabrication and substrate selection. Figure 1 shows this relationship and the lattice constants of some candidate substrate materials for the InGaAiN system are indicated by the dotted lines [11]. We can see from this figure that DH structures can be configured using lattice-matching. Although sapphire is similar to GaN, it does not have a wurtzite structure. The lattice-mismatch between GaN and (0001) sapphire is 13.8% as shown in Table 1. In addition, this table also includes thermal expansion mismatch which is as important as lattice constant for epitaxial growth. In particular, sapphire with various types of commercially available planes are compared in Table 2. This table shows the relationship of orientation, lattice-mismatch and crystallographic symmetry between a GaN epitaxial film and a sapphire substrate. From the viewpoints of lattice-mismatch and crystallographic symmetry, (01J•0) sapphire seems the most suited to GaN growth. The c-axis of a GaN film grown on a (01 i0) sapphire substrate inclines to that of this substrate. This means that twins may generate in an epitaxial film. This is the only disadvantage of a (01 i0) plane in comparison with a (0001) plane. Lattice-mismatch of NdGaO3 with an orthorhombic crystal structure is calculated in Table 1. This structure has been regarded as pseudo-cubic because the lattice constants along with the a- and b-axes are almost the same
Data Loading...
