<title>Silicon p-i-n photodiode with low values of dark current</title>

Abstract

Dark current dependence of silicon p-i-n photodiode on the p-type layer location depth at the photodiode crystal back. It was revealed that the smallest specific values ofdark current is obtained at 6 -9 pm p-type layer depth.Three mechanisms that explain the obtained results were considered: dislocational, metal impurities and strain influence on the metal -semiconductor edge (back contact).Reliability of p-i-n photodiodes on the silicon base is provided by many factors, including stability of photoelectrical parameters. Dependence of photodetector parameters on noises that are generated by semiconductor crystal is very considerable because, as it is know&, it is device noise that determines its threshold sensitivity. Noise level in general case is defined by level of dark current that has some constituents. Proposed paper considers questions of generation constituent decreasing.In general case, dark current that passes through p-n junction (ii), is defmed by the sum of diffusion current in neutral region (ID) and generation current in depletion region (IG): I = 'D 'G . The depletion region in p-i-n photodiodes that are optimised for registration of wave lengths 2 1 pm is usually spread out to the entire bulk of photodiode crystal, thus the neutral region is practically absent and it can be neglected. As the generation current is proportional to the depletion region width (1)1 then dark current in the examined case is determined by generation constituent and it is proportional to space-charge region width: I 'G W.At the duration of elaboration and production of certain photodiodes 2,3 was observed the effect of dark current reduction against the background of increasing oflayer thickness that is situated at the back ofthe photodiode crystal and is isotypical to it. The main appointment of the layer is resistance reduction at the semiconductor -metal contact. In certain cases device sensitivity in long-wave range depends on dimentions and location ofp-type layer at the crystal back '. P-i-n photodiodes were produced from p-type silicon with impurity concentration 1 10" -4 10" cm'. The construction optimisation was carried out in order to register radiation of Si spectral characteristic maximum, namely A = 0.8 -O.9tm, and also to register radiation with wave length 2 = 1.05 .tm.The obtained results have shown that photodiode dark currents, optimised to receive radiation with wave length 2 = 1 .05 tim, are more sensitive to the thickness of isotypical (pttype) with crystal (p-type) sublayer at its back then photodiodes, optimised to register more short waves. For instance, at p-layer thickness of 1-2 pm and work voltage 150 V specific values of dark current constitute 1 .0 -10.0 .tA/cm2 at the average value 3 -5 A/cm2 (Fig.l). If the type layer thickness composes 2 -4.5 p.m than dark current specific values of photodiodes produced by means of the same technology constitute 0.9 -3.0 .tA/cm2. Further increase of the pt-type layer thickness at the photodiode crystal back more than 4 mkm requires increase of the B diff...

Study of the Charge Carrier Collection Coefficient of Silicon p-i-n Photodiodes

“…In practice, a significant reduction in the substrate thickness is a difficult technological task due to the reduced mechanical strength of the wafers. However, it is possible by forming thinnings on the back side of the crystal by chemical-dynamic polishing [19] in a shape that corresponds to the responsive element, provided that the proper thickness of the crystal periphery is ensured, which will play the role of stiffeners [20]. The described thinning on the back side of the substrate can be seen in Figure 5.…”

Estimation on frequency characteristics of a photodiode determined by the motion of charge carriers in the space charge region on the surface generation of carriers

“…The frequency characteristics of photodiodes determine their fast operation and ability to register the smallduration pulse signals. These characteristics are mainly determined by the time of flight of photogenerated charge carriers through the the space-charge region (SCR) [1][2][3]. Therefore, the task to properly estimate these characteristics is actual for the modern pulse optoelectronic technique, in particular for the construction of semiconductor fast-acting p-i-n photodiodes.…”

Estimation of frequency characteristics of photodiode determined by motion of charge carriers in the space-charge region

“…In addition, characteristics of photodiode are determined by the external applied voltage and wave length of the used optical radiation. In the case of its absorption, only in its SCR and at negligibly small distances around it, for example, in a p-i-n photodiode, frequency characteristics are determined, mainly, by the time-of-flight of the generated charge carriers through the SCR [1][2][3][4].…”