Analysis of the optimized low-nonlinearity lateral effect sensing detector

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1 Jounal of hysics: Confeence Seies Analysis of the optimized low-nonlineaity lateal effect sensing detecto To cite this aticle: Saeed Olyaee et al J. hys.: Conf. Se Related content - Neual netwok appoximation of nonlineaity in lase nano-metology system based on TLMI Saeed Olyaee and Samaneh Hamedi - The TD mode of opeation of LESD I Abdulhalim - Optimizing intedigitated contact scheme of GaN-based light-emitting diodes Bin Cao, ei Wang, Zhiyin Gan et al. View the aticle online fo updates and enhancements. This content was downloaded fom I addess on 6//9 at :53

2 3d Intenational hotonics & OptoElectonics Meetings (OEM ) Jounal of hysics: Confeence Seies 76 () 4 doi:.88/ /76//4 Analysis of the optimized low-nonlineaity lateal effect sensing detecto Saeed Olyaee, Ali Bidang, Mahdie Izadpanah Nano-photonics and Optoelectonics Reseach Laboatoy (NORLab), Faculty of Electical and Compute Engineeing, Shahid Rajaee Teache Taining Univesity (SRTTU), Lavizan, , Tehan, Ian s_olyaee@sttu.edu Abstact- In this pape, the cuent time delay (TD) and the voltage diffeence (VD) modes fo some pactical lateal effect position sensing detectos ae investigated, simulated, and compaed. Some advantages of the cuent time delay mode ae moe linea esponse, independent position fom magnitude and fequency, backgound illumination-independent esponse, and no need to signal nomalization. Key wods: Lateal effect position sensing detectos, voltage delay, time delay.. Intoduction osition-sensing detectos ae known as simple photodiodes capable of detecting centoid of light beam position. Thee is an impotant featue fo SDs due to no need to have contact with specimen being inspected. osition infomation is calculated fom photocuent signal magnitude by these detectos. Fo designing these detectos with high esolution, the most effective method is to ceate Schottky baie with suface diffusion method []. When an optical spot incidents on the detecto suface, electic chage is geneated popotional to the light intensity at the collision egion. Electic chage passes fom esistive laye and collected as the photocuent by electodes. It is divided between two teminals with an invese elation to the distance of optical spot fom electodes. Applying full evese bias to LE, the thickness of depletion egion inceases, diffusion cuent deceases to zeo and suface egeneation is stopped. To achieve best pefomance quality, the photodiode should be able to absob maximum photons in depletion egion. It means photons should not be absobed anywhee except depletion egion befoe passing it. So, when a p-n junction is illuminated by the optical spot, little enegy is saved in space chage egion. Unde evese bias, this light enegy will move hoizontally to the electodes mounted next to the junction. This phenomenon is called lateal effect fist pesented by Schottky in 93, but has not been developed much []. In 959, Wallmak used this theoy pactically [3]. He designed a device including a p-n junction. By illuminating light beam to the suface, a position-dependent voltage diffeence is geneated between the contacts [3]. The position sensing detectos have many applications in distance measuement, machine vision, atomic foce micoscope, suface shaping, obots, tacking lase beam, etc. They ae classified into ublished unde licence by Ltd

3 3d Intenational hotonics & OptoElectonics Meetings (OEM ) Jounal of hysics: Confeence Seies 76 () 4 doi:.88/ /76//4 two types: lateal effect position sensing detectos and fou-quadant position sensing detectos [4], with some similaities and diffeences to each othes, physically and pactically []. Voltage delay mode has been widely used to detemine the position of optical spot until now. As shown in Figue, if optical spot incidents on the detecto suface, I and I photocuents ae geneated at electodes and then convet to voltage, so the optical spot position can be obtained by calculating voltage diffeence between two electodes. The disadvantage of this method is diametedependent voltage in optical spot led to detecto nonlineaity. In this pape, cuent time delay mode is poposed to make detecto moe linea. In this method, as the optical spot incidents on the detecto suface, a cuent has been geneated. The cuent eaching time, fo each electode is diffeent, depending on the optical spot position. So, thee is a time diffeence between two signals eached to teminals. Hee, the diamete of optical spot has no effect on signals aival time. Fo example, if eaching signals oscillate synchonous, the optical spot will mount at the cente of detecto suface. The est of the pape is oganized as follows. In section, a bief investigation is pesented about LEs, thei dynamic equations and electonic cicuit based on the [7]. The simulation esults fo thee pactical LEs ae discussed in section 3 and the conclusions ae dawn in the final section. Figue. One-dimensional detecto stuctue.. Lateal effect position sensing detectos (LESDs) Lateal effect position sensing detectos include a unifom esistive laye mounted in one o two sides of semiconducto sub-laye with high esistivity (Figue ). Output Ix XB hotocuent XA Spot Output Ix -Laye I-Laye N-Laye Com Resistive Length Lx Figue. Schematic of lateal effect position sensing detectos (LEs) [5].

4 3d Intenational hotonics & OptoElectonics Meetings (OEM ) Jounal of hysics: Confeence Seies 76 () 4 doi:.88/ /76//4 In one-dimensional case, thee is a pai of electodes to obtain position signals at the two ends of esistive laye, and in two-dimensional case, two pais of electodes mount on the edge of the detectos mutually. The active aea (o esistive laye) includes a p-n junction geneated photocuent due to light collision to the suface (photovoltaic effect). LEs have unifom big stuctues with an anode and a cathode. Because these detectos do not depend on optical spot diamete magnitude, detectivity quality is independence of thei distance fom the object. Thee ae two models fo LEs: one-dimensional and two-dimensional models, i.e. the ability to detect -D o -D positions. Usually in detecto analysis, fist -D case is investigated and then it can be genealized to -D case. When an optical spot mounts on the detecto suface, photocuent is geneated by each electode, depending on the distance of beam centoid fom electodes. So, with measuing output, the beam position can be also measued [6]. The equation of - D position detectivity, based on Figue is given as [7]: I I X S () I I whee I and I ae the output cuents of electodes. Afte calculating cuents, we can wite them in the fom of voltage diffeence between two electodes. As shown in Figue 3, Eq. can be ewitten as: V V X S V V () and the time delay between two signals can be obtained by Eq. 3: X S t (3) whee t is the time delay between the two signals. Figue 3. Conveting output cuents to voltage. When the optical spot incidents on the LE suface, thee will be a caie distibution led to a gadient in excess caie concentation. The optical spot will stat to spead in a Gaussian manne contolled by the diffusion coefficient and the ecombination lifetime without any lateal o tansvese extenal electic fields. So, the obtained cuent diffeence can be in the fom of voltage diffeence between electodes. This idea was pesented fist by Walmak. In this method, cuent diffeence led to voltage diffeence mode while time delay causes time diffeence and moe linea esponse. To simulate LE, we used Lucovsky Equation [6-7]: 3

5 3d Intenational hotonics & OptoElectonics Meetings (OEM ) Jounal of hysics: Confeence Seies 76 () 4 doi:.88/ /76//4 V x J s w qev c V [exp( ) ] k T w t B qe w g( x, t) (4) whee V is the lateal photo-voltage, Js is the tansvese satuation cuent density, is the esistivity of the p-doped egion and w is the thickness of the p-doped egion. p In small signal analysis, because q e V << k B, it can be ignoed and the Eq. 4 can be ewitten as: V c V qe g( x, t) (5) x w t w With nomalizing elation 5 (to the VG max and by the time constant RC) it can be witten [7]: V V t x whee R R G se sh V g ( x, t) V V is nomalized to V V (epesented by ( x, t) ) and G max V G V ( x, t) g ( x, t ) V G m (6) G is nomalized photon flux distibution in the detecto suface [5]. Equation 5 is valid fo any LEs with R se a simila atio. We can eplace a simila elation fo cuent distibution not voltage instead of Rsh Eq. 5. Fo this eason, the initial and bounday conditions should be consideed as: V (,) (, ) (, x V t V t ) (7) And fo geneated photocuent in two electodes, we have: V i,, x x (8) x By expanding Eq. 5 in Fouie seies fom and by conveting voltage to cuent, the cuents will be: i ( )sin( o I xp t ) (9) i ( )sin( I xp t ) () x is the nomalized position fo detecto length and and denote phase delays fo signals. By expanding Fouie seies aound mid point, the slope of linea egion is given [7]: L cosh( ) cos( i) S () sin( i) i sinh( ) Eq. shows that S is linealy popotional to fequency and detecto length. Fo linea egion slope, in voltage diffeence mode, we have [7]: cosh( i ) cos( ) S L i sin( i ) sinh( ) S and S ae the slopes of time delay and voltage diffeence modes [7]. 3. Simulation esults The functions esulted fom Eqs. and ae shown in Figue 4. The lineaity of time delay mode can be easily infeed in compaison to voltage diffeence mode.with R se and R sh, we can use these elations fo any photodetectos. We know when an optical spot appoaches to detecto teminals, () 4

6 3d Intenational hotonics & OptoElectonics Meetings (OEM ) Jounal of hysics: Confeence Seies 76 () 4 doi:.88/ /76//4 voltage diffeence deceases. As shown in Figue 4, ove a dynamic fequency ange, time delay mode is moe linea than voltage diffeence mode. Figue 5 shows the simulation esults fo S393 detecto. This detecto is moe linea in time delay mode than S3979 detecto ove a lage fequency ange. The simulation esults fo S393 detecto ae also shown in Figue 6. It can be concluded that this detecto has bette pefomance compaing two othe detectos. Figue 7 is a 3-dimensional gaph fo voltage diffeence and time delay mode signals. As shown in this figue, in voltage diffeence mode, signals will satuate at the edges nomalized slope fo VD Mode nomalized slope fo TD Mode nomalized fequency LE nomalized fequency LE3979 (a) (b) Figue 4. Nomalized slope with espect to the nomalized fequency fo (a) VD and (b) TD modes in S3979 detecto..5 - nomalized slope fo VD Mode.5 nomalized slope fo TD Mode nomalized fequency LE393 (a) nomalized fequency LE393 (b) Figue 5. Nomalized slope with espect to the nomalized fequency fo (a) VD and (b) TD modes in S393 detecto. 5

7 3d Intenational hotonics & OptoElectonics Meetings (OEM ) Jounal of hysics: Confeence Seies 76 () 4 doi:.88/ /76// nomalized slope fo VD Mode.5..5 nomalized slope fo TD Mode nomalized fequency (a) nomalized fequency LE393 (b) Figue 6. Nomalized slope with espect to the nomalized fequency fo (a) VD and (b) TD modes in S393 detecto..8.4 Eo[mm] Y[mm].. (a)..4 X[mm].6.8 (b) Figue 7. The eo of position detection in X- and Y-axes fo (a) VD and (b) TD modes in S393 detecto. Eo[mm] Y[mm]....4 X[mm] Conclusion In this pape we have compaed thee pactical LESDs based on the analysis epoted by Abdullhalim in 4 [7]. Accoding to the obtained esults, time delay mode has moe advantages compaing to the voltage diffeence mode. Also with having the atio R se / Rsh, fo any lateal effect position sensing detectos, TD and VD modes elations can be witten and investigated. Hee, S393 has moe lineaity in the esponse compaing to the S393 and S

8 3d Intenational hotonics & OptoElectonics Meetings (OEM ) Jounal of hysics: Confeence Seies 76 () 4 doi:.88/ /76//4 Refeences [] etesson G, Lindholm L, 998, osition sensitive light detectos with high lineaity, IEEE Jounal of Solid State Cicuits,Vol.sc-3, No.3. [] Schottky W,93, On the oigins of photoelectons in Cu O-Cu photocells, hys. Z., 3, pp [3] Wallmak J T, 957, A new semiconducto photocell using lateal photoeffect, oc. IRE, pp [4] Makynen A,,"osition-sensitive devices and senso systems fo optical tacking and displacement sensing applications", Depatment of Electical and infomational Engineeing univesity of Oulu. [5] H X Song, X D Wang, L Q Ma, M Z Cai and T Z Cao Design and pefomance analysis of lase displacement senso based on position sensitive detecto (SD) J. hys. D: Appl. hys. 48 (6) 7 [6] Lucovsky G, 96, hotoeffects in nonunifomly iadiated p n junctions, J. Appl. hys., pp [7] Abdulhalim I, 4, Device physics of the time-delay mode of opeation of optoelectonic lateal effect position sensos, J. hys. D: Appl. hys. 37 (4)