Experimental research IMPATT-diodes on heterostructures &Gel -zGaAs showed that the interphase boundary is noted with high thermal and radiation resistance. It is shown t h a t sucli diodes are an equivalent alternative IMPATT-diodes with type of Schottky barrier.
The paper is concerned with the results of investigation of structure defects in gallium arsenide and Alo.3Gao.7As epitaxial layers. I t was found that structure defects It is known that quality and reliability of the semiconductor devices are considerably determined by structure perfection of epitaxial layers, used for fabrication of the active elements (DZHAFAROV; ASTAKHOV et al.). It is well proved on germanium and silicon devices. Recently, structure defects have been thoroughly studied in gallium arsenide and its solid solutions to determine the reasons for the injections lasers degradation ( PANISH) .I n the present work the microstructure of GPE grown gallium arsenide films and Al,Gal-,As films grown by LPE method is compared with the parameters of the Schottky diodes formed on this films.Monocrystalline gallium arsenide, doped by tellurium to 2 -lo1* ~m -~ was used as substrate. The concentration in GaAs and Ga,Al1_,As epitaxial layers ranged about 10l5 + 10l6 cni-3, film thickness was 3-12 pm. Samples were etched in HNO, to H,O = 1:2 with citric acid addition. MIM-8 microscope was used for the metallographic analysis. Layer by layer film and substrate etching showed that in the chosen concentration range dislocation density in epitaxial layers is roughly independent on the doping level both for GaAs and Alo.3Gao.yAs films, and is essentially determined by substrate properties. Both films have also had the diamond -shaped structure defects (KONAKOVA et al.) with size from 1 pm to 30 pm. The same type of defects was observed ir, highly doped substrates. During the film was layer by layer etched up to interface the transformation of diamond -shaped etching figures into well expressed dislocation loops with diameters of 1-10 pm was observed (Fig. l a , b). It proves with evidence that the growth of impurity enriched phase in the form of diamondshaped inclusions takes place mainly on dislocations and dislocation loops (penetrating from substrate).Study of GaAs epitaxial layers with the same doping level shows that thin (d < 5 p m ) films have higher density of structure defects than relatively thick (d -12 pm) ones.We suggest this fact to be due to the doping gradient in the vicinity of the film -substrate interface, greater affecting relatively thin films.
Epitaxial multilayer GaAs structures find wide application for the fabrication of active elements of UHF microelectronics (IMPATT diodes, varactors, etc.) /1 to 4/. But in some cases the efficiency of such devices turns out to be considerably lower than estimated. The presence of a tunneling-recombination current component in the pre-breakdown region is the reason causing the decline of the UHF diode output parameters, for example IMPATT /5/.In the present work the structural perfection and electrical characteristics ++ +++ of multilayer GaAs epitaxial films with a "buffer" layer (Bs) type n-n and n -n-n -n structure parameters a r e presented in the table.-n + ++ +++ and without BS (n-n+++) were investigated. The main epi-Metallographical investigations of the GaAs epitaxial layers showed that in samples with BS, the dislocation density is an order of magnitude higher than in those without BS. In Fig. 1 (see on the photo pages before the Short Notes part) we give microphotographs of the film-substrate interface in the structure without BS and with BS. It is obvious that the structural perfection of the interface in the second case is higher than that in the first one. A high local density of dislocations in A-type structures leads to a higher concentration of the doping impurity and may cause its segregation, i. e. the appearance of inclusions of the second phase.The diameter of such structural imperfections is 5 to 50 p m and their 4 2 density is 10 cm . Thus, the probability to find such an inclusion in the working area of the diode is rather high. Localization of a strong field in the 10 physica (a)
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