On Tue, 15 May 2012 10:21:06 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Hi, all, > >Most of the time I just model photodiodes as current sources with >parallel capacitances, and put in any deviations by hand afterwards. At >the moment I have an application where I need to do rather better than >that, to explore the tradeoff between speed, bias voltage, and quantum >efficiency. (It may wind up with custom photodiodes.) > >The only thing I've found in the free literature is a strange paper from >some Serbian guys who use, like, 100 subcircuits to model one >photodiode. > >I'm sure it would be good for my soul to do an approximate analytic >solution of carrier transport as a function of device geometry and stick >that in as a behavioural model, but at the moment I'm too busy and too >lazy. > >Does anybody have a reference to a photodiode model that includes >transit time, high level injection, and bias dependence? > >Thanks > >Phil HobbsHi Phil, Do you have a link to that paper? Maybe I can decipher it. Or, better yet, describe the effect and maybe I can directly model it. (I need something fun to do :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
SPICE model for photodiodes including transit time effects?
Started by ●May 15, 2012
Reply by ●May 15, 20122012-05-15
Reply by ●May 15, 20122012-05-15
Joerg wrote:> > Phil Hobbs wrote: > > [...] > > > The reason I care is that larger photodiodes have different behaviour > > for photocurrent generated in different places. For obvious reasons > > they can't have a nice thick metal layer over top of the epi like > > ordinary diodes. The epi is heavily doped to improve its conductivity, > > so there's not much E field inside it, and the electrons have to travel > > mostly by diffusion. Heavy doping also reduces the carrier mobility. > > > > That tends to make regions of the diode far from the contact slow down > > quadratically with increasing diameter, which is something I care about > > a lot. The quadratic slowdown is masked in datasheet curves, because > > the RC delay is going quadratically with diameter as well. However, the > > RC delay is position-independent, so there's a big difference in > > performance for things like noise cancellers, which rely on the > > photocurrent being a faithful replica of the incident beam power no > > matter where it happens to land. > > > > It also lowers the average speed so it's probably not just a concern to > engineers trying to cancel noise.That's true. I'm just a couple of orders of magnitude more sensitive to it, which makes me the photodetection equivalent of the miner's canary. ;)> > > There are Schottky-barrier photodiodes and double Schottky barrier > > (interdigitated) photodiodes, which have metal top layers, but not in > > any decent sizes like 1-3 mm diameter. Some clever sub-wavelength > > interdigitated structure could probably be nearly independent of > > position and polarization, but now is not the time to launch a research > > project on photodiode design, though it might be fun eventually. > > > > A group of scientists from Japan had that patented and I wouldn't be > surprised if some company started making them. Usually they are called > interdigital electrodes. > > ... oh, this might be it: > > http://jp.hamamatsu.com/products/light-source/1008/pd383/index_en.htmlInterdigitated PDs have been around for 30 years that I know about--classically, they have two opposing Schottky barriers, so you have to bias them above reach-through (when the potential well between the barriers is tipped over enough by the applied E field that the minimum reaches the position of one of the barriers, which then effectively goes away). The Hamamatsu ones are doing something different, because they work at low bias voltages. I was talking mostly about using a sub-wavelength grating for the fingers, which seems like it could be insensitive to polarization and position. Cheers Phil Hobbs> > -- > Regards, Joerg > > http://www.analogconsultants.com/-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 15, 20122012-05-15
Jim Thompson wrote:> > On Tue, 15 May 2012 10:21:06 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >Hi, all, > > > >Most of the time I just model photodiodes as current sources with > >parallel capacitances, and put in any deviations by hand afterwards. At > >the moment I have an application where I need to do rather better than > >that, to explore the tradeoff between speed, bias voltage, and quantum > >efficiency. (It may wind up with custom photodiodes.) > > > >The only thing I've found in the free literature is a strange paper from > >some Serbian guys who use, like, 100 subcircuits to model one > >photodiode. > > > >I'm sure it would be good for my soul to do an approximate analytic > >solution of carrier transport as a function of device geometry and stick > >that in as a behavioural model, but at the moment I'm too busy and too > >lazy. > > > >Does anybody have a reference to a photodiode model that includes > >transit time, high level injection, and bias dependence? > > > >Thanks > > > >Phil Hobbs > > Hi Phil, Do you have a link to that paper? Maybe I can decipher it. > > Or, better yet, describe the effect and maybe I can directly model it. > > (I need something fun to do :-)Hi, Jim, Thanks. What I'm trying to get a handle on is the effect of transit time in the epi, which is position-dependent, vs. the substrate, which basically isn't. Small photodiodes are RC-limited, but bigger ones aren't, and I need to figure out what's going on. I can do C-V measurements to get the doping density vs depth, but the lateral effects are harder to get a handle on. (If I were a silicon device guy, I'd be further ahead than I am--I just know enough to be dangerous, and not enough to be really clear about it.) So something like contact p+ epi-------------------------------p+ epi--------- nu (very low doped N) nu nu nu N++ contact metal_metal_metal_metal_metal_metal where the top layer is both an RC transmission line (which looks like diffusion) and also really diffusive, due to the low fields inside. If there's a standard way to model transit time and diffusive transport in SPICE, that would be a win. Modelling high level injection in the nu layer would be interesting too, but maybe that's too much work and too many adjustable parameters. Thanks again Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 15, 20122012-05-15
Jim Thompson wrote:> > On Tue, 15 May 2012 10:21:06 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >Hi, all, > > > >Most of the time I just model photodiodes as current sources with > >parallel capacitances, and put in any deviations by hand afterwards. At > >the moment I have an application where I need to do rather better than > >that, to explore the tradeoff between speed, bias voltage, and quantum > >efficiency. (It may wind up with custom photodiodes.) > > > >The only thing I've found in the free literature is a strange paper from > >some Serbian guys who use, like, 100 subcircuits to model one > >photodiode. > > > >I'm sure it would be good for my soul to do an approximate analytic > >solution of carrier transport as a function of device geometry and stick > >that in as a behavioural model, but at the moment I'm too busy and too > >lazy. > > > >Does anybody have a reference to a photodiode model that includes > >transit time, high level injection, and bias dependence? > > > >Thanks > > > >Phil Hobbs > > Hi Phil, Do you have a link to that paper? Maybe I can decipher it. > > Or, better yet, describe the effect and maybe I can directly model it. > > (I need something fun to do :-) >The paper is at http://electrooptical.net/www/sed/photodiode/LazovicSpiceModelsOfFastPhotodiodes100Subcircuits.pdf (or http://tinyurl.com/6u9844p ). Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 15, 20122012-05-15
On Tue, 15 May 2012 14:08:00 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Jim Thompson wrote: >> >> On Tue, 15 May 2012 10:21:06 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >> >Hi, all, >> > >> >Most of the time I just model photodiodes as current sources with >> >parallel capacitances, and put in any deviations by hand afterwards. At >> >the moment I have an application where I need to do rather better than >> >that, to explore the tradeoff between speed, bias voltage, and quantum >> >efficiency. (It may wind up with custom photodiodes.) >> > >> >The only thing I've found in the free literature is a strange paper from >> >some Serbian guys who use, like, 100 subcircuits to model one >> >photodiode. >> > >> >I'm sure it would be good for my soul to do an approximate analytic >> >solution of carrier transport as a function of device geometry and stick >> >that in as a behavioural model, but at the moment I'm too busy and too >> >lazy. >> > >> >Does anybody have a reference to a photodiode model that includes >> >transit time, high level injection, and bias dependence? >> > >> >Thanks >> > >> >Phil Hobbs >> >> Hi Phil, Do you have a link to that paper? Maybe I can decipher it. >> >> Or, better yet, describe the effect and maybe I can directly model it. >> >> (I need something fun to do :-) >> > >The paper is at >http://electrooptical.net/www/sed/photodiode/LazovicSpiceModelsOfFastPhotodiodes100Subcircuits.pdf > >(or http://tinyurl.com/6u9844p ). > >Cheers > >Phil HobbsThanks! The only Lazovic paper I found was a horrible scan with a watermark that obscured all the important stuff. I'll take a look and see if I can decipher it. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 15, 20122012-05-15
Jim Thompson wrote:> > On Tue, 15 May 2012 14:08:00 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >Jim Thompson wrote: > >> > >> On Tue, 15 May 2012 10:21:06 -0400, Phil Hobbs > >> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> > >> >Hi, all, > >> > > >> >Most of the time I just model photodiodes as current sources with > >> >parallel capacitances, and put in any deviations by hand afterwards. At > >> >the moment I have an application where I need to do rather better than > >> >that, to explore the tradeoff between speed, bias voltage, and quantum > >> >efficiency. (It may wind up with custom photodiodes.) > >> > > >> >The only thing I've found in the free literature is a strange paper from > >> >some Serbian guys who use, like, 100 subcircuits to model one > >> >photodiode. > >> > > >> >I'm sure it would be good for my soul to do an approximate analytic > >> >solution of carrier transport as a function of device geometry and stick > >> >that in as a behavioural model, but at the moment I'm too busy and too > >> >lazy. > >> > > >> >Does anybody have a reference to a photodiode model that includes > >> >transit time, high level injection, and bias dependence? > >> > > >> >Thanks > >> > > >> >Phil Hobbs > >> > >> Hi Phil, Do you have a link to that paper? Maybe I can decipher it. > >> > >> Or, better yet, describe the effect and maybe I can directly model it. > >> > >> (I need something fun to do :-) > >> > > > >The paper is at > >http://electrooptical.net/www/sed/photodiode/LazovicSpiceModelsOfFastPhotodiodes100Subcircuits.pdf > > > >(or http://tinyurl.com/6u9844p ). > > > >Cheers > > > >Phil Hobbs > > Thanks! The only Lazovic paper I found was a horrible scan with a > watermark that obscured all the important stuff. I'll take a look and > see if I can decipher it. >Thanks. I think my stackup was probably backwards--on reflection, it would be pretty perverse to use p-type epi, since its carrier mobility is so much lower. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 15, 20122012-05-15
On Tue, 15 May 2012 14:01:19 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Jim Thompson wrote: >> >> On Tue, 15 May 2012 10:21:06 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >> >Hi, all, >> > >> >Most of the time I just model photodiodes as current sources with >> >parallel capacitances, and put in any deviations by hand afterwards. At >> >the moment I have an application where I need to do rather better than >> >that, to explore the tradeoff between speed, bias voltage, and quantum >> >efficiency. (It may wind up with custom photodiodes.) >> > >> >The only thing I've found in the free literature is a strange paper from >> >some Serbian guys who use, like, 100 subcircuits to model one >> >photodiode. >> > >> >I'm sure it would be good for my soul to do an approximate analytic >> >solution of carrier transport as a function of device geometry and stick >> >that in as a behavioural model, but at the moment I'm too busy and too >> >lazy. >> > >> >Does anybody have a reference to a photodiode model that includes >> >transit time, high level injection, and bias dependence? >> > >> >Thanks >> > >> >Phil Hobbs >> >> Hi Phil, Do you have a link to that paper? Maybe I can decipher it. >> >> Or, better yet, describe the effect and maybe I can directly model it. >> >> (I need something fun to do :-) > > >Hi, Jim, > >Thanks. What I'm trying to get a handle on is the effect of transit >time in the epi, which is position-dependent, vs. the substrate, which >basically isn't. > >Small photodiodes are RC-limited, but bigger ones aren't, and I need to >figure out what's going on. I can do C-V measurements to get the doping >density vs depth, but the lateral effects are harder to get a handle >on. (If I were a silicon device guy, I'd be further ahead than I am--I >just know enough to be dangerous, and not enough to be really clear >about it.) > >So something like > > contact >p+ epi-------------------------------p+ epi--------- >nu (very low doped N) >nu >nu >nu >N++ contact >metal_metal_metal_metal_metal_metal > >where the top layer is both an RC transmission line (which looks like >diffusion) and also really diffusive, due to the low fields inside.Is the top contact just around the edge? In that case, the p+ epi resistance is max for light that hits the center, less closer to the edge. For slow pulses! Yikes. Does anybody apply a contact grid to the top, like a solar cell? -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●May 15, 20122012-05-15
John Larkin wrote:> > On Tue, 15 May 2012 14:01:19 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >Jim Thompson wrote: > >> > >> On Tue, 15 May 2012 10:21:06 -0400, Phil Hobbs > >> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> > >> >Hi, all, > >> > > >> >Most of the time I just model photodiodes as current sources with > >> >parallel capacitances, and put in any deviations by hand afterwards. At > >> >the moment I have an application where I need to do rather better than > >> >that, to explore the tradeoff between speed, bias voltage, and quantum > >> >efficiency. (It may wind up with custom photodiodes.) > >> > > >> >The only thing I've found in the free literature is a strange paper from > >> >some Serbian guys who use, like, 100 subcircuits to model one > >> >photodiode. > >> > > >> >I'm sure it would be good for my soul to do an approximate analytic > >> >solution of carrier transport as a function of device geometry and stick > >> >that in as a behavioural model, but at the moment I'm too busy and too > >> >lazy. > >> > > >> >Does anybody have a reference to a photodiode model that includes > >> >transit time, high level injection, and bias dependence? > >> > > >> >Thanks > >> > > >> >Phil Hobbs > >> > >> Hi Phil, Do you have a link to that paper? Maybe I can decipher it. > >> > >> Or, better yet, describe the effect and maybe I can directly model it. > >> > >> (I need something fun to do :-) > > > > > >Hi, Jim, > > > >Thanks. What I'm trying to get a handle on is the effect of transit > >time in the epi, which is position-dependent, vs. the substrate, which > >basically isn't. > > > >Small photodiodes are RC-limited, but bigger ones aren't, and I need to > >figure out what's going on. I can do C-V measurements to get the doping > >density vs depth, but the lateral effects are harder to get a handle > >on. (If I were a silicon device guy, I'd be further ahead than I am--I > >just know enough to be dangerous, and not enough to be really clear > >about it.) > > > >So something like > > > > contact > >p+ epi-------------------------------p+ epi--------- > >nu (very low doped N) > >nu > >nu > >nu > >N++ contact > >metal_metal_metal_metal_metal_metal > > > >where the top layer is both an RC transmission line (which looks like > >diffusion) and also really diffusive, due to the low fields inside. > > Is the top contact just around the edge? In that case, the p+ epi > resistance is max for light that hits the center, less closer to the > edge. For slow pulses! Yikes.Worse than that. Lots of them have a contact only at one edge, which (assuming diffusion dominates) makes them 4 times slower at the opposite edge than in the centre.> > Does anybody apply a contact grid to the top, like a solar cell?Various people have made PDs with indium-tin oxide electrodes, or very thin metal on top of the epi. It costs you some efficiency, and ITO isn't that great a conductor anyway. (It's a pure hole conductor, for one thing.) A subwavelength grid, properly designed, could do a pretty good job, but might be a bit narrowband and would certainly be more money, because you'd need real masks. Photodiodes can practically be made with a stencil and spray paint. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 16, 20122012-05-16
In article <4FB26652.CA4BA472@electrooptical.net>, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> Hi, all, > > Most of the time I just model photodiodes as current sources with > parallel capacitances, and put in any deviations by hand afterwards. At > the moment I have an application where I need to do rather better than > that, to explore the tradeoff between speed, bias voltage, and quantum > efficiency. (It may wind up with custom photodiodes.) > > The only thing I've found in the free literature is a strange paper from > some Serbian guys who use, like, 100 subcircuits to model one > photodiode. > > I'm sure it would be good for my soul to do an approximate analytic > solution of carrier transport as a function of device geometry and stick > that in as a behavioural model, but at the moment I'm too busy and too > lazy. > > Does anybody have a reference to a photodiode model that includes > transit time, high level injection, and bias dependence?I don't know of any such models, not having looked, but it occurs to me that the issue has been extensively researched by CERN, both for direct radiation detectors, and for CCDs. The CCD master is Janesick: Scientific Charge-Coupled Devices, James R. Janesick, SPIE Press, 2001, 906 pages. This may be a source of ideas. Joe Gwinn
Reply by ●May 16, 20122012-05-16
Joseph Gwinn wrote:> > In article <4FB26652.CA4BA472@electrooptical.net>, > Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > > > Hi, all, > > > > Most of the time I just model photodiodes as current sources with > > parallel capacitances, and put in any deviations by hand afterwards. At > > the moment I have an application where I need to do rather better than > > that, to explore the tradeoff between speed, bias voltage, and quantum > > efficiency. (It may wind up with custom photodiodes.) > > > > The only thing I've found in the free literature is a strange paper from > > some Serbian guys who use, like, 100 subcircuits to model one > > photodiode. > > > > I'm sure it would be good for my soul to do an approximate analytic > > solution of carrier transport as a function of device geometry and stick > > that in as a behavioural model, but at the moment I'm too busy and too > > lazy. > > > > Does anybody have a reference to a photodiode model that includes > > transit time, high level injection, and bias dependence? > > I don't know of any such models, not having looked, but it occurs to me > that the issue has been extensively researched by CERN, both for direct > radiation detectors, and for CCDs. > > The CCD master is Janesick: > > Scientific Charge-Coupled Devices, James R. Janesick, SPIE Press, 2001, > 906 pages. > > This may be a source of ideas. >Thanks, I have JJ's book. (We corresponded on the CCD mailing list for some years, on and off.) CCDs are a different regime though--small and slow, vs. big and fast. Cheers Phil Hobbs> Joe Gwinn-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
