Dash, G N

Mishra, I P

Mishra, J K

Pattanaik, S R

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Indian J. Phys. 77A (4). 387-391 (2003)/<Q ^ o i eIJPA \Optically controlled noise a^d small-signal behaviour of READavaliinche diodeG N Dash', J K MisAa*, I P Mishra and S R PattanaikP G Department of Physics, Sambalpur Ipiversity, Jyoti Vihar, Sambalpur-768 019, Orissa. IndiaV?•P G Department of Physics, G M Co|ege (Autonomous), Sambalpur-768 004, Orissa, India B-mail . |ndashC4>rediffmail.comReceived 10 August 2001, accepted 25 February 2003A bstract : A new analytical model to study the effect of optical radiation on the noise behaviour of a Read type IMPATT diode is presented. The application of this method to a Si-Read diode reveals some interesting features of reduction in the resonance like noise peak due to optical injection.Keywords : IMPATT, optical, radiation, noise.PACS Nos. : 85/ kk,73.40, -cIMPA1T (IM Pad Avalanche Transit Time) diodes constitute a major source of microwave power. The impact ionisation process responsible for power generation in an IMPATT di­ode is also responsible for the generation of avalanche noise in the diode. With the modernisation of device technology, realisation of low noise in semiconductor devices has become an important aspect for research [1,2]. In recent years, optical control of microwave properties in IMPATT diodes has gained revived interest. A good numbers of work on optical control of IMPATT diodes like optical switching [3,4], tuning [5,6] and injection locking [7,8] have been reported. In addition, optical carrier injections leading to an improvement in oscillator noise have also been demonstrated [9,10], More recently, Herbert and Davis [11] have suggested tunneling and/or optical injec­tion as a means of reducing noire in IMPATT diode. The forma" (tunnel injection) has already been considered by us [12] witii interesting results. We now consider the optical injection in this paper for possible means of achieving low noise in IMPATT diode. We have confined our discussion on the small signal regime and the Read model because both of these per­mit analytical solutions; analytical solutions although consid­ered qualitative in nature, are highly instructive and clearly show directions for improvements. Using our analytical model, we have studied the noise behaviour of a Si Read diode at different level of optical radiation. Our results show some in­teresting features of increase in the level of optical radiation on the noise behaviour of Read type IMPATT diodes.PhotonfluxV n p 7t p"x=0 XiFigure 1. Schematic diagram of the double Read IMPATf diode show­ing the doping pattern of different layers.A generalised Read diode model is considered which can be used to investigate the properties of not only the n-type (n*vnp*) and p-type (n p^rtp*) Read diodes but also the prop­erties of double Read (n’vnp7tp+) diode in presence of optical radiation ks shown in Figure 1. The steady state carrier conti­nuity equation in presence of optical radiation can be written as [for definition please refer to the list of symbols]Corresponding Author©2003IACSmd J A x )^  Ondn<<x) + a p J  p{x) + qG„p(^x)^ n J  p{x) +CX pJ p{x) + qC,ip{x) . (1)The optical generation rate may be expressed as [ 13]K a M n  -11« « - « p  -«<,The total current density J, follows directly from eq. (7) asG N Dash, J K Mishra, IP  Mishra and S R PattanaikA h v(2)dp -  dpi, d„ = J -J 'p , at x = X| (3a)and dn =d'„,, d p =J -J'„, at X = X2 , (3b)where d'ps=dp,+q^ Ni^ -^ ~“'‘"') (4a)and (4b)y and y are the reverse hole and electron saturation currentps nsu„ —a„ —a„rt p a(5)a „ -c tpd n ~ a p - « aRewriting eq. (6) and keeping in mind that. J [a ,  ] = K ia ^  )(6)g(“»-“pp* _ lia„~ap)Xf,««. .  Pop,{^-R)....................................................where <Pn -  — number  of photons striking perunit area per unit time. Eq. (1) is solved to obtain an expressionfor total current density J = J  „ + J  p ,\t\ presence of opticalradiation, with the boundary conditionsy » y ' + +apJ'p,)\j a A a „ - a p ) e - ‘‘“^ ' _ iJa„-ap)Xg (X)densities at the respective boundaries. Rearranging eq. (1),multiplying with the integrating factor ^<"»'“p^^and integrat­ing between the limits x, and Xj with appropriate boundary conditions mentioned above, we get(y -  J'„,On - « pThis expression for 7 in the absence of optical illumination, is the same as that of Elta and Haddad (14J in the absence ol tunneling. This value of current density in presence of optical radiation Is used to estimate an effective ionisation rate (equal for both electrons and holes), which takes into account the actual values of experimentally determined ionisation rates used in the above analysis, may be defined as that value of ionisation rate, which will generate the same J  in the genera tion region as by the actual experimentally determined values of ionisation rates. An expression for may be obtained in the following way.For the case of , the steady state continu­ity equation may be written asdJp ix)  dxop^Integrating this between the limits x  ^and Xj with appropriate boundary conditions and rearranging, the effective ionisation rate may be expressed as"Dividing both sides of eq. (5) by and puttingofj -X , = the avalanche region width, we have( y - y ; , ) e ‘“'’-“ '’ "^* ~ j'p , -------------i l lJx„( 10)This value of effective ionisation rate is used to solve the Read equation to obtain the expressions for the device proper­ties. Thus, the use of a^jf removes the error arising out of the assumption of equal Ionisation rates for electrons and holes in Read equation.For the noise analysis the noise current density is consid­ered to have three components namely J^ , due to critical elec­tric field necessary to maintain a steady avalanche, J^, due to AC field caused by y„^and a displacement noise current den­sity y^ An expression for is obtained following the method of Hines [15] asJ n o - l2qJBvl/2( 11)Optically controlled noise and small-signal behaviour of READ avalanche diode 389Die expression for and displacement current density are obtained by solving Read equation under optical illumination following our method described in [12] as2Xg Eg„a^^J icoTg + 2 ( l-a ,^ X g ) (12);,ndyrf |J3)where = x^ tv ^  and the expression for the amplitud| of AC noise field in the generation region £  is the same a | in 112). Now, following a similar procedure as in [12], the n»an square noise voltage per bandwidth can be obtained as< V,: >B2qJ(o^t I ai.JfrfSin(9^ a ^ ( l-c o s ^ ,^ )  ,V eThe small-signal properties are computed from the diode impedance by defining the diode admittance =1/Z^ from which the diode conductance (G) and the diode resistance are obtained respectively as the real part of and Z^. It may be mentioned here that the diode conductance and diode re­sistance which shows negative values for a certain range of frequency (defined as bandwidth), are useful parameters to assess the small-signal performance of the diode.The above analytical method is used to study the noise behaviour of a Si-based n^prip^ Read diode at different level of optical injections. The total width of the diode is taken as 1 pm and the avalanche region width as 0.2 pm. The reverse saturation electron and hole current densities ,/^  and J are taken as IpA/m^ each. The optical absorption peak wavelength and the optical absorption coefficient at this wavelength for Si are taken from f 13]; X = 0.8pm and a  =10'm The operating current density is chosen to be 7 =5 x 10^  Am i  The generation region electric field required to generate this value of 7, in presence of optical radiation, is determined by an iterative sub­program in the following way. First, a trial value of the electric field is chosen and the total current density 7 in presence of‘ optical radiation, is computed following eq, (8). If this value differs from the chosen 7, then the electric field is suitably varied, over several iterations, until the computed 7 is equal to the chosen 7 within an accuracy of 0.05%. The percentage ofoptical current density J^pt / J is then determined. This pro­cess is repeated for different (|)^  values and the mean square noise voltage as well as the small-signal parameters like diode conductance and diode resistance is estimated in each case. The results arc presented in Table 1 and Figures 2-4.Hgure 2. Variation of device negative conductance as a function of frequency for different level of optica! injection.5 10 50 100Frequency (GHz)Figure 3. Variation of mean square noise voltage per bandwidth us a function of frequency for different level of optical injection390 G N Dash, J K Mishra, IP  Mishra and S R PattanaikFigure 2 shows the frequency versus conductance plots for the Si-Read diode for different level of optical injection. It can be seen from Table 1 and Figure 2 that the device negative conductance (-Gp at optimum frequency (^) decreases steadily with increase in optical injection. Further, it is observed from Figure 2 that the bandwidth of the device decreases consider­ably as the optical injection level increases. It can also be observed from Table 1 that the device property like negativeresistance (- )and negative conductance (-G ) at optimum frequency, which are indicative of power outpuf from the de­vice, decreases with increase in photon injection. Figure 3I ’able 1. Small signal and noise properties of the Si Read IMPATF diode at different level of optical illumination.«v,/> /fl) alf^ NM a t/ ,(%) (lO'^V s^) (GHrKlO^ * S/m^)(lO“n  m2) (lO'^V s^)O.U 7221.1 8.062.2 2.055.5 0.36210.0 0.18132343438423.513.313.102.602.091 .260.9690.9210.5470.3325.933.883.871.780.8651790153013301240999shows the plots for variation of the mean square noise voltage as a function of frequency at different level of optical injec­tion. It is observed from this figure that, a sharp peak of 7.22 X 10^2 y 2 5 resonant frequency is recorded for a verylow level of photon injection. However, this noise peak drasti­cally reduces to 8.06x10 V^s when the level of photon injec­tion is nominally increased to 1% (Table 1). It is also observed from Figure 3 and Table 1 that as the level of photon injection increases, the noise peak further decreases and at about 5% of optically generated current the peak completely vanishes. This can be understood by noting that, under ideal condition with negligible reverse saturation current, the generation region behaves like a purely reactive circuit with 0 and and in parallel with each other. This gives rise to a sharp peak of and hence (<v^  ^>/B) as co co^ . However, due to optical injection the reverse saturation current increases which in­creases the resistive component (R^) of the generation region. This increases the third term in the denominator of 112] which in turn suppresses the peak in (<v^^ >/B) curve. It can also be seen from Tabic 1 that the value of mean square noise voltage at optimum frequency shows a steady decrease from 3.88 X10 V^s to 0.86 X 10 ‘^  V^s with increase in the level of photon injection from 0.1% to 10%. The noise measure defined as the ratio < > A/ 4BkT(-Z^), is considered as an indicator ofnoise power to useful power ratio. This quantity has been plotted as a function of frequency in Figure 4 for different level of optical radiation. Each of the curves shows a minimum at a frequency, which is approximately twice or more than that of the optimum frequency (/p. This frequency (noise measure minimum) may be chosen for operation of the diode for very low noise. However, the power output at this frequency would be drastically low. In addition, it is observed that the noise measure minimum constantly increases with increase in thelevel of optical radiation. Thus, this frequency corresponding to noise measure minimum is unsuitable for operation it one intends to harness the benefit of optical radiation. On the other hand, at optimum frequency, the noise measure is observed to68 72 76 80F req u en cy  (G H z)F ig u re  4. N o ise  m easu re  as a fu n c tio n  o f  freq u en cy  fo r d iffe ren t level o f  o p tic a l in je c tio n .constantly decrease (Table 1) with increase in level of optical injection. 1'his is partly due to increase in optimum frequency and partly due to decrease in mean square noise voltage w ith  increase in optical radiation. Thus, a suitably tailored dose o f  photon for operation at the optimum frequency, will not only reduce the noise to a tolerable level but will keep the powci output at a moderate level.An analytical model to study the noise as well as small- signal behaviour of a Read diode in presence of optical radia­tion is presented in this Note. This method can be applied to  any type of Read diode. A Silicon-based IMPATT Read diode is studied with this new model at different level of optical ra­diation. The results show that it is possible to control the device properties by a suitable level of photon injection s u c h  that the mm-wave properties do not degrade appreciably, ai the same time the noise reducing to a tolerable level.Optically controlled noise and small-signal behaviour of READ avalanche diode 391AcknowledgmentThe authors wish to acknowledge the Department of Science ami Technology, Government of India for financial support ol this work through a major research project (SP/S2/M-12/98).ReferencesV[ 11 G N Dash, J K Mishra and A K Panda Solid-State Elecuome^ 1473 (1996) ,i|2 | J K Mishra, A K Panda and G N Dash IEEE Trans. Electron Devices ED-44 2143 (1997)A nnexure13] H W Yen, M K Bainoski, R G Hunspergci and R I’ Melvipc Appl. Phys. Lett. 31 120 (1977)[41 R A Kichl IEEE Trans Electron Devices ED-27 42(i (19S0;151 A J Seeds, J F Singleton, S P Brunt and J R Forrest IEEE J. U j^t Wave Tech. LT-5 403 (1987)(61 C Chiu and J Freycr Froc. Inst. Elec. En^. 131 28 (1984)17) A j Seeds and J R Forrest Electnm Lett. 14 829 (1978)|K| FI W Yen Appl Fhys. Lett. 36 680 (1980)19] A J Seeds and J R Fonesi Electron U*tt. 17 865 (1981)[101 PM Pitner, R J Gulmann and J M Borrego Frot. In.st. Ela Eny.‘ 128 149 (1982)1111 D C  Herbert and R G Davis IEEE Trans Electron Devices ED- 47 197 (2000)I ! 2j G N Dash, J K Mishra and S K Nayak IE IE Tech. Review 16 243(1999)113] S M Sze Physics o f Semiconductor Devices (New Delhr Wielcy Eastern ), 2nd Edn. (1987)114] M B Ella and G 1 Haddad IEEE Trans. Electron Devices ED-25 694 (1978)115] M Fi Hines IEEE Trans. Electron Devices ED-13 158 (1966)AIIccf.Grhhv7/IV77/'*LKFopldRRKA'CIIZa/'r0)(0Varea of the diode band widthdrill legion eapaeitance geneiation region eapaeitanee opiimum Ircqucney: diode eonducianee at /6': Planek’s eonslam  : photon energyconduclK)n current density lor elections , electron leverse salutation euirenl density : condueiion eurreni density lot holes hole reverse saturation current density generation region iiulucianee average incident optical powci electronie chargeleflcetion coellieient of the surtaecgeneration region resistancesaturated drill velueily of eairierswidth ol the depletion layerdistance in depletion legiondull region widthgeneration region widthdrill legion impedancediode impedancegenetaliuii legion impedancediode resistance at /6'optical absorption coellieient field dctivalive ol a.„ ionisation lale for electrons ionisation rale foi holes ficqiiency ot light angulai licqiiency t>l A C  : geneiation legion angular liequency lime between successive collisions pcrmitiviiy of tlie semicoiukutor tiansil angle foi dull tcgion

Optically Controlled Noise and Small-Signal Behaviour of Read Avalanche Diode

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Optically Controlled Noise and Small-Signal Behaviour of Read Avalanche Diode

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