tag:blogger.com,1999:blog-19092890.post8689559723238969700..comments2024-03-28T15:26:27.432+02:00Comments on Image Sensors World: Trap-Assisted Injection Gain in Organic PhotoconductorsVladimir Koifmanhttp://www.blogger.com/profile/01800020176563544699noreply@blogger.comBlogger8125tag:blogger.com,1999:blog-19092890.post-31378939931556406932020-02-13T00:46:01.972+02:002020-02-13T00:46:01.972+02:00Sure, photocurrent gain is an old thing.
Understa...Sure, photocurrent gain is an old thing.<br /><br />Understanding, where it comes from, at the device/microscopic level, and device/aplication implications, are not always understood well.<br /><br />People usually assume "ohmic" injection contact, that magically supplies the missing carriers. <br />Injection contacts are not "ohmic", they rely on non-ideal effects turning on this extra injection, leading to all sorts of unusual device behaviors.<br />Maxim Ershovhttps://www.blogger.com/profile/12629698883604865273noreply@blogger.comtag:blogger.com,1999:blog-19092890.post-39288265654907399172020-02-12T20:04:11.119+02:002020-02-12T20:04:11.119+02:00Photocurrent gain is not new in image sensors. Th...Photocurrent gain is not new in image sensors. The old vidicon tube used antimony trisulfide in this mode with voltage-variable gain and a gamma of 2/3 from the non-linear effect of induced electric fields from the accumulating charge.Davehttps://www.blogger.com/profile/00631712355502733371noreply@blogger.comtag:blogger.com,1999:blog-19092890.post-10984405523570190792020-02-12T19:08:32.676+02:002020-02-12T19:08:32.676+02:00The basic mechanism is very simple.
The light exci...The basic mechanism is very simple.<br />The light excites the carriers (let's say, electrons) from their "seats" in the volume of the "photoconductor" (a "seat" may be an impurity, a quantum well/dot, or a trap).<br />Photoexcited electrons are extracted form the photoconductor volume into "collector" - hence, you need to have applied voltage, to create electric filed, to extract them.<br />That's primary photocurrent.<br />Then an uncompensated positive charge is left in the photoconductor, that increases the electric field or lowers the barrier at the injection contact. <br />More carriers are injected form the "emitter", and flow through the photoconductor into the collector.<br />That's secondary, or multiplied photocurrent.<br />If probability of their capture to the vacant "seat" is low, many secondary electrons flow through the detector in response to one photoexcited electron.<br />That's photocurrent gain.<br />It can be small (smaller than one), or large (1-10-100-1000-...) - if capture probability is low.<br />Eventually the vacant "seat" gets an electron, and equilibrium is re-established.<br /><br />This mechanism produces a wealth of interesting and counter-intuitive (at a first glance) physical phenomena in such photodetectors.<br /><br />As en example - impurity photodetectors were notorious for very slow transient, history-dependent photoresponse, nonlinear ("hook") photoresponse, etc.<br />It made them very difficult to use and calibrate in space.<br />Until Fuks explained this and showed how to deal with this.<br />Similarly - with quantum well infrared photodetectors.<br />At very low temperatures and low background radiation, they behave in a weird way, which puzzled people for a long time.<br /><br />CMOS image sensors operate very differently, so these phenomena and problems are, luckily, not present there.<br /><br />One interesting effect that I am sure you will observe in your photodetectors is negative capacitance (but not at any operating conditions).Maxim Ershovhttps://www.blogger.com/profile/12629698883604865273noreply@blogger.comtag:blogger.com,1999:blog-19092890.post-15829581569709074182020-02-11T23:55:58.058+02:002020-02-11T23:55:58.058+02:00Thanks for the info, never heard about it. I will ...Thanks for the info, never heard about it. I will have a closer look at these works.Anonymoushttps://www.blogger.com/profile/08229385072346684626noreply@blogger.comtag:blogger.com,1999:blog-19092890.post-56678588157831907152020-02-11T10:41:17.527+02:002020-02-11T10:41:17.527+02:00I think that the effects described in this paper, ...I think that the effects described in this paper, including large photocurrent gain and its physical mechanism, are very similar to what's happening in impurity photodetectors, and in quantum well infrared photodetectors.<br /><br />Search for papers by Boris Fuks for impurity photodetectors, and for papers by Maxim Ershov (me) for QWIPs.<br /><br />Responsivity drop at high power, at high frequency, injections effects, <br />transient photoresponse with two time constants, etc.Maxim Ershovhttps://www.blogger.com/profile/12629698883604865273noreply@blogger.comtag:blogger.com,1999:blog-19092890.post-51344196514367184692020-02-10T11:42:14.504+02:002020-02-10T11:42:14.504+02:00Thanks for quoting my paper ! Raphael Clerc.Thanks for quoting my paper ! Raphael Clerc.Anonymoushttps://www.blogger.com/profile/08229385072346684626noreply@blogger.comtag:blogger.com,1999:blog-19092890.post-23784326512322939812020-02-10T11:31:08.263+02:002020-02-10T11:31:08.263+02:00Sorry, my mistakeSorry, my mistakeVladimir Koifmanhttps://www.blogger.com/profile/01800020176563544699noreply@blogger.comtag:blogger.com,1999:blog-19092890.post-51660349706666268002020-02-10T11:25:08.409+02:002020-02-10T11:25:08.409+02:00And the first author ?And the first author ?Anonymousnoreply@blogger.com