Substrates semi-insulating

The main advantages that compound semiconductor electronic devices hold over their siUcon counterparts He in the properties of electron transport, excellent heterojunction capabiUties, and semi-insulating substrates, which can help minimise parasitic capacitances that can negatively impact device performance. The abiUty to integrate materials with different band gaps and electronic properties by epitaxy has made it possible to develop advanced devices in compound semiconductors. The hole transport in compound semiconductors is poorer and more similar to siUcon. Eor this reason the majority of products and research has been in n-ty e or electron-based devices. 

When both donors and acceptors are present, compensation results, whereby the electrons supplied by the donor are given to the acceptor. Thus, the free carrier concentration can be considerably reduced below that expected from introducing a known donor or acceptor if the opposite type of dopant is unintentional. For example, semi-insulating (SI) InP (used as a substrate for epitaxial growth) can be made by incorporating low levels of Fe3+ as a deep acceptor (reduced to Fe2+) to compensate for unintentional n-type doping in the sample [19]. 

A GaN substrate would be a help in this respect but it would need to be semi-insulating. In addition, GaN has a poor thermal conductivity and is not very suitable due to this negative material property. Aluminum nitride substrates may become the substrate of choice for GaN high-frequency applications. It has a reasonable thermal conductivity and is intrinsically semi-insulating but only time will tell. 

Fig. 8. Energy below the conduction band of levels reported in the literature for GaAs. Arrangement and notations are the same as for Figs. 4 and 5. Notations not defined there are epitaxial layer on semi-insulating substrate (EPI/SI), boat-grown (BG), vapor phase epitaxial layer on semi-insulating substrate (VPE/SI), melt-grown (M), molecular beam epitaxy (MBE), horizontal Bridgman (HB), irradiated with 1-MeV electrons or rays (1-MeV e, y), thermally stimulated capacitance (TSCAP), photoluminescence excitation (PLE), and deep level optical spectroscopy (DLOS).

Fig. 22. Magnetic circular dichroism (MCD) spectra of (a) undoped semi-insulating GaAs substrate and (b), (c) of epitaxial Gai t Mn As films at T = 55 K and B = 1 T. The spectrum of GaAs is magnified ten times because the signal is weaker than that of Gai rMn As (Ando et al. 1998).

In EP-A-00686S2 photodiodes are formed by diffusing indium into a layer of semi-insulating CdTe which covers an HgCdTe substrate. 

An epitaxially grown p-type Hgo.8Cdo.2Te layer 12 is produced on a CdTe semi-insulating substrate 1 and the p-type layer is doped by n-type impurities to produce n-type regions 15a and 15b. A protective film 21 is formed over the p-type layer but not over the n-type regions. 

The cross-talk between adjacent photodiodes formed in an HgCdTe layer on a semi-insulating CdTe substrate, is reduced in JP-A-2248077 (NEC Corp., Japan, 03.10.90) by providing n+-type regions in the CdTe substrate at regions corresponding to regions between the photodiodes. 

A microcircuit may be described as a collection of devices each consisting of an assembly of active and passive components, interconnected within a monolithic block of semiconducting material [4]. Each device is required to be isolated from adjacent devices in order to allow for maximum efficiency of the overall circuit. Furthermore within a device, contacts must also be electrically isolated. While there are a number of methods for isolating devices in a circuit (reverse-biased junctions, mesa isolation, use of semi-insulating substrates, and oxide isolation), the isolation of active components of a single device is almost exclusively accomplished by the deposition of an insulator. 

InP FETs Ion implantation has been successfully applied to fabricate FETs on semi-insulating InP substrate. In FETs with a noise figure as low as 3.5 dB at 12 GHz have been fabricated (52). 

Semi-insulating polycrystalline silicon (SIPOS) is found in many applications, including the electrical passivation of high-voltage planar devices, emitters in heterojunction transistors, and thin-film silicon solar cells on cheap foreign substrates. SIPOS is usually deposited by CVD onto a Si substrate. The composition of the SIPOS SiOx Aim varies from x = 0 (polycrystalline or amorphous Si) to X = 2 (Si02). The untreated film consists of a nonrandom mixture of Si and Si02 and relatively small amounts of an intermediate oxide of SiOi A (A = 0.14) [75, 76]. 

GaAs substrate has a very high resistivity (is semi-insulating), providing sufficient transistor-to-transistor isolation without the need for reverse-biased isolation junctions. 

Other Backgating is problem in semi-insulating substrates... 

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