Leakage diodes

Figure 17. (a) Typical reverse characteristics of low leakage diodes passivated with BPDA-PDA (measurements performed in PFPE environment at 25 °C). (b) Views of the same probed diode in PFPE oil, before (top image) and after (bottom image) high voltage measurements. 

Semiconductor laser diodes are widely used in CD players, DVDs, printers, telecommunication or laser pointers. In the structure, they are similar to LEDs but they have a resonant cavity where laser amplification takes place. A Fabry-Perot cavity is established by polishing the end facets of the junction diode (so that they act as mirrors) and also by roughening the side edges to prevent leakage of light from the sides of the device. This structure is known as a homojunction laser and is a very basic one. Contemporary laser diodes are manufactured as double heterojunction structures. 

Schottky diodes can have almost lOx the leakage current of a good Schottky. In this case, that was what was ultimately confusing the switcher IC to break into chaos every now and then. We replaced it with a quality diode and everything was fine thereafter. 

Incidentally, Schottky diodes do not have any reverse recovery current issues, but they do have some body capacitance, which can produce similar effects. However, that fear has always proven to be exaggerated. I have personally not seen any application having a performance issue explicitly related to a bad Schottky. The only exception was a case where the leakage current of the Schottky was so high, it was prematurely tripping the current comparators inside the switcher IC. And there was also a reliability issue once, concerning the dV/df rating of a commercial Schottky. Both these issues are discussed elsewhere in this book. 

Note that the a-Si H protected diode has more than one order-of-magnitude lower leakage current than the diode protected by Si02. After heating the device at 500°C for hour (a typical metallization treatment), the leakage current is still much lower than the standard oxide-passivated diode. 

The Schottky barriers were excellent diodes for films annealed at 600 °C, with turn on voltages of 0.6-0.8V and minimal reverse bias leakage.48 However, many of the contacts on the as-deposited films gave large reverse bias currents and nearly ohmic responses. This behavior is indicative of degeneracy of the semiconductor because of a high carrier density resulting from native defects. The improvement in the diode behavior of the annealed films is attributed to enhanced crystallinity and reduction of defects. 

The electrical properties of an anodic oxide are found to depend on the formation conditions and subsequent treatments such as annealing. As-prepared anodic oxides show high leakage currents and a diode-like behavior known from anodic oxides of valve metals. A short high-temperature anneal, which removes the bound hydroxyl, reduces the leakage current to values typical of thermal oxides, as shown in Fig. 5.9. 

The imager of EP-A-0406696 is made up of a compositionally graded p-type base layer and a compositionally graded cap layer in which pn-junctions are formed. The structure has a small amount of leakage current and a large diode impedance. 

An imager having mesa-shaped photodiodes overlayed with a layer of passivation which contains a fixed charge is presented in WO-A-8707083 (Santa Barbara Research Center, USA, 19.11.87). The charge creates an inversion layer within the surface of the mesa walls, thereby enlarging the pn-junction and reducing the diode leakage-current of each photodiode. 

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