Junction diodes leakage current

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. 

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. 

The data of Fig. 3 show the reverse-bias I- V characteristics for two representative p-n junctions. The one labeled Iox was passivated with thermal oxide, the one labeled /a.Si H was passivated with a-Si H. It is striking that the leakage current of the a-Si H-passivated junction is two orders of magnitude lower than that of the Si02 -passivated diode. 

Another important phenomenon to be checked is the leakage current of shallow junction diodes. The leakage current provides valuable information about the quality of the Si-W interface and whether unallowed amounts of silicon are consumed during the selective tungsten deposition process. Again, one can expect that blanket tungsten gives less problems here because of the presence of the adhesion-barrier layer. 

Before discussing DLTS, it is appropriate to talk about some device parameters that are affected by these impurities. The main parameters are the recombination and generation lifetimes because they affect junction leakage current, device switching speed, light emitting diode efficiency and a number of other device performance indicators. 

Ghezzo et al [13] reported on ion implanted planar p-n junction 6H-SiC diodes fabricated by ion implantation of B into n-type SiC with the donor concentration of 9x 1015cm 3. The implantation was performed at 25 °C and 1000°C followed by a 1300°C post-implant furnace anneal. The diodes had an ideality factor of 1.77 at room temperature, the reverse leakage current of 1 O 10 A cm 2 at -10 V and the reverse breakdown voltage of -650 V. 

Suzuki and co-workers [14,15] fabricated P-SiC p-n junction diodes using a mesa structure. The tum-on voltage at room temperature was 1.2 V and a reverse leakage current of 5 pA was measured at - 5 V. This leakage current is much greater than that for a-SiC diodes. Both parameters were severely degraded at elevated temperatures. Edmond et al [16] and Avila et al [17] have also produced p-n junction diodes in P-SiC. These diodes were made by ion implantation and operated up to 673 K. 

Reverse current density is important in deterrnining the power that a device consumes when in the off state as it determines the effective resistance of the device in reverse bias. Hence reverse current is also referred to as leakage current. From Equation 3.24, the reverse current is carried by drift of minority carriers from the lightly doped side of the junction (that is the side having the higher minority carrier density) toward the heavily-doped side. If one assumes a p -n diode (the p-type side is very heavily doped) then Equation 3.24 becomes ... 

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