INVESTIGATION OF TRANSFERRED-ELECTRON AMPLIFIER DIODES ... Bound... · INVESTIGATION OF TRANSFERRED-ELECTRON AMPLIFIER DIODES WITH A ... mental study of Gunn diodes which have

R948 Philips Res. Repts 31, 257-277, 1976

INVESTIGATION OF TRANSFERRED-ELECTRONAMPLIFIER DIODES WITH A DOPING NOTCH *)

by J. MAGARSHACK, P. HARROP and A. RABIER

Abstract

A computer model has been developed which simulates both small- andlarge-signal performances ofTransferred- Electron Amplifier (TEA) diodesstabilised by a doping notch. Experimental confirmation of the simula-tion has been sought by means of devices which have been fabricatedto include doping notches of different depths. Measurements have beentaken with the device biased in both polarities so that the doping notchappears at either the cathode or the anode ofthe diode, and a comparisonis made between the results. Experimental results are reported concerningthe small-signal impedance, noise figure, large-signal impedance, maxi-mum added power, efficiency and intermodulation-product performancein both polarities. Indication is given of the large-signal stability andbandwidth of negative resistance encountered in these devices. Theresults, both of the computer simulation and measurements, suggestthat, for cathode-notch devices, more efficient amplifier diodes can beproduced by using a shallow notch structure and that this configurationis not optimum for lowest noise figure. Furthermore, a useful inter-modulation performance is achieved by using an anode-notch configura-tion.

Introduction

Reflection amplifiers using Gunn diodes are finding applications in bothnarrowband systems at frequencies which are as yet prohibitive to transistoramplifiers (> 12 GHz) and as wideband amplifiers capable of producing~edium power (> 100mW at 1 dB gain compression).1t is the need for ampli-fiers of the latter category that has formed the basis for the present study.It has previously been established 1-4) that the form of the diode doping

profile plays a role of fundamental importance in determining the character-istics of this type of amplifier. In particular, it has been shown 4) that relativelylow noise figures (10.9 dB at 12 GHz) can be obtained by tailoring the profileso that a uniform field is established throughout the active layer. This profileis characterized by a doping notch near the cathode.The purpose of this article is to report results of a theoretical and experi-

mental study of Gunn diodes which have doping notches. The influence ofthe notch, its depths and position at either the anode or the cathode, on

*) This work has been supported by Centre National d'Etudes et Télécommunications(CNET LANNION).

258 J. MAGARSHACK, P. HARROP AND A. RABIER

parameters such as maximum added power, efficiency, noise figure and inter-modulation have been investigated.

The article will be presented in three sections, the first of which will describethe computer model that has been used to simulate diode behaviour under bothsmall- and large-signal conditions, thus enabling the assessment of the efficienciesof diodes of different doping profiles. The second section will include a de-scription of experimental results, at small and large signals, measured with thedevice biased such that the notch appears either at the cathode or at the anode.These results include measurements of impedance, maximum added power,efficiency and noise figure. The final section will present conclusions whichcan be drawn from the work and will indicate the type of doping profile whichis considered necessary for a specific application whether this be primarily aquestion of lowest possible noise figure, highest possible efficiency or lowestintermodulation products.

bE bne - = J(E) - q n veE) + q D(E) - ,bt bx

(2)

1. The computer simulation

This section will first give a brief account of the classical technique ofsimulation of this type of active device before analysing the computer resultswhich have been obtained with the doping notch at the cathode and finallywith the notch at the anode.

1.1. Definition and description of the model

The method is based on the unidimensional numerical solution of Poisson'sequation and basic continuity incorporating appropriate values of veE) andD(E) 5).

The model of the device is placed in a resistive circuit and is subjected to ad.c. bias and an alternating signal whose amplitude and frequency are variables.The d.c. bias may either be a constant-voltage source, which is the case in thelarge signal simulation, or a constant-current source, which is the case in thecalculation of the stationary electric field.

The two fundamental equations are presented in the following form.

bE q- = - [n - no(x)] ,bx e

(1)

where no(x) = the donor concentration which corresponds to the doping profileat a position x into the sample,

n = electron concentration.

INVESTIGATION OF TEA DIODES WITH A DOPING NOTCH 259

where J(E) = current density in the sample,veE)= electron velocity,D(E) = diffusion coefficient.

The analytical representation of veE)which has been adopted 6) is

!-loE + vo(E/Eo)4v(E)------

- 1+ (E/Eo)4 '(3)

where Eo = threshold field.There remains some doubt as to the exact dependence on electric field of thediffusion coefficient of electrons in GaAs 5.7-11). The analytical expressionused in this study is based on the calculations of Hammer and Vinter 10) andis the following:

Do + Ds[(E - Ep)/Ee]4D(E) = -1-+-[-(E--E-

p)-/E-

e-]4-. ' (4)

where Do = 130 cmz/s; D, = 25 cmz/s; Ep = 0 kV/cm; Ee = 5.78 kV/cm.The doping profile is introduced into the calculations through

where NF = doping concentration in the :flat region,N; = doping concentration in the notch,Cl = width of notch,

Kç, Kz = coefficients which describe the form of the notch, i.e. theslopes of doping in and out of the notch.

The equations (3), (4) and (5) are substituted in eqs (1) and (2) which aresolved using the numerical technique of finite differences. Thus information isobtained concerning the static-field distribution, small-signal impedance as afunction of frequency and large-signal impedance evolution with increasingapplied r.f. power at discrete frequencies of interest.The data obtained in this manner have led to the estimation of the level of

third-order intermodulation products since it is possible to deduce the coeffi-, cients of an nth-degree polynomial of the dependence of r.f. current on r.f.

voltage.If

n

then the insertion into this expression of two equal-amplitude voltage wavesof frequencies Wl and Wz (5 MHz apart) permits the deduction of the ratio


of power in the third-order intermodulation frequencies (2fl - f2 and 2f2 - fl)to that in the fundamental frequencies (fl and f2). So that

P3 (~a3 V3)2Pr = (2 al V+ ¥ a3 V3)2 .

(6)

1015ç-------------~--:;----,I 1.38·'015cm-3

2 1.1 .1015cm-3

3 8.8 ·1014.cm-3

1/:;.=:-..::.:-:::':'=.~2-=--:'::_-:-/_.

3

The knowledge of al and a3 thus enables the ratio P3/Pr to be calculated fordifferent values of incident power.

1.2. Simulation of cathode-notch diodes. Influence of ratio of the doping levelsin the flat to notch regions (r)

It is useful to define a parameter, r, which is the ratio of the doping concen-tration in the fiat region to that in the notch.

The performance ofthree differentdoping profiles (fig. la) has been examined.These three profiles have different static electric-field distributions as shown infig. lb. Profile (1) (r = 2.42) presents an electric-field distribution which risesrapidly to a field well in excess of the threshold field at the edge of the notch

Fig. la. Doping profiles used in simulations: profile 1, r = 2.42, profile 2, r = 1.88. profile 3.r = 1.47.

2345678910-L(pm)

Fig. lb. Computed electric-fields configurations in the diodes for each of the three profiles.

15

10


after which it decreases and is below threshold at the anode. Profile (2)(r = 1.88) generates an electric field which rises to 11 kV/cm at the edge ofthe notch and then remains approximately constant throughout the active layer.The electric field produced by profile (3) (r = 1.47) rises to 6 kV/cm at theedge of the notch and continues to rise steeply until it has a value of 25 kV/cmat the anode.~n order that a realistic appraisal of their amplifier efficienciescould be made,

the diodes doping concentrations were adjusted so that each sample dissipatedthe same d.c. power and therefore each sample has the same operating tem-perature (200°C). Furthermore, the small-signal impedances of the three de-vices from 7 to 11 GHz, which ate presented in fig. 2a, are seen to be verysimilar.The large-signal impedances, at 7, 9 and 11 GHz, along with the equivalent

circuit used in the calculations, are presented on fig. 2b for each profile. Theparameter on the curves is added power which is marked at maximum gain

• r=2.4.2• r= T.88... r = T.4.7

Fig. 2a. Computed small-signal impedance as a function of frequency for each of the threeprofiles.

Lé1~16coswt

ar =2.4.2o r= T.88I>.r= T.47

Fig. 2b. Computed large-signal impedance, at 7, 9 and 11 GHz, along with the equivalentcircuit used.


and at its maximum value. It is clear from the figure that there is generally anexpansion of gain into a 50 n load, which occurs before the diode begins tosaturate. However, there are several observations which distinguish betweenthe performances of the three simulated devices.Profile (1) produces the smallest values of maximum added power, and

therefore efficiency, throughout the frequency range 7-11 GHz. It does,however, present no gain expansion at 7 and 9 GHz although at 11GHz thereis gain expansion.Profile (2) produces intermediate values of maximum added power and the

evolution of its large-signal impedances takes the form of wide loops corre-sponding to significant gain expansion into a 50 .Q load.Profile (3) generates the largest values of maximum added power and the

large-signal impedance loops are generally more closed. Table I presents themaximum added power at 7, 9 and 11 GHz obtained from the three simulateddevices.

TABLE I

frequency r = 1.47 r = 1.88 r = 2.42

7 GHz 29.3 mW 16 mW 3.2mW9 GHz 113.7mW 81.4 mW 7.5mW11 GHz 93.4 mW - 43.5 mW

It is evident from table I that the structure which is capable of being the mostefficient is that which has the shallowest notch.In addition, it is interesting to note that the form of the impedance loop

presented by the device with smallest r is also that which is most conducive tolinear medium power and wideband amplifier design. A circuit could be de-signed for this device which would present, throughout the band 7-11 GHz,an impedance which would minimize the effect of gain expansion whilst stilltaking advantage of the higher added power.

1.3. Simulation of anode-notch diodesThe majority of the results which have been obtained in this study have been

measured on devices biased so that the notch appeared at the cathode. In thecourse of the measurements, it became apparent that the device could operateequally well and in certain cases with more interesting results, under reversedpolarity, i.e. with the notch at the anode. It was therefore interesting to try tosimulate this mode of operation with the existing computer model. This iseasily effected by replacing x by (L - x) in expression (5) so that


[ ((L - X»)2] NF - N, [ (L-X- (})]n(x) = Ne exp - Kl + N; + 2 v 1+ tanh K

2

(7)

Figure 3 represents the result of this attempt applied specifically to the caseof one of the epitaxial layers which was realized (If 823). The figure includesboth the small-signal impedance (5.5-18 GHz) and the large-signal impedanceevolution at 9 GHz.The static electric-field distribution for this configuration is such that a high-

field region exists at the anode with the field exceeding its threshold valueapproximately halfway along the sample.The large-signal results indicate a much reduced gain-expansion phenomenon

and a value of maximum added power which is comparable with the cathode-notch configuration.The field distribution of the anode-notch device is very similar to that of a

device with a doping profile which steadily decreases from the cathode to theanode as has been previously reported 12) to give very stable diodes. The evolu-tion of the impedance of such a device as the signal drive increases can be com-pared qualitatively to the corresponding behaviour of a cathode-notch(constant

Jl823D(E) MIRCEAV=16.4V

Fig. 3. Computed small-signal impedance of anode-notch diode and large-signal evolution(added power as parameter) at 9 GHz.

TABLE 11


field) device by considering the variation of the electric field as it is modulatedby the signal.For the uniform-field device (notch at the cathode) as the signal increases,

it drives the field into the high negative differential mobility region at eachpoint in the sample. The negative resistance has a tendency to increase there-fore and as the drift velocity increases, the reactance changes as well.

For the anode high-field device (notch at anode, or sloping down profile)the signal drives the field into the negative-mobility region only in a small partof the sample. In the region near the cathode the signal drive produces a morepositive resistance, so that the total resistance of the sample saturates towardsa smaller value of the negative resistance.

2. Experimental results

Devices have been fabricated with a variety of different doping profiles whoser values range from 1.2-3.5. The diodes were mounted in S4 packages andcharacterized in 50 Q coaxial support which was water-cooled.The first part of this section will discuss results taken with the notch at the

cathode and the second part will describe a similar set of measurements takenfrom the same devices biased so that the notch appears at the anode.

Principle parameters of the epitaxies

epitaxy length of doping cone. doping cone,number active layer in that region in notch r

((LID) (1014 cm=") (1014 cm=")

823 11 7.5 2.2 3.5824 11 8.0 5.0 1.6825 11.5 8.5 6.0 1.4826 11 9.0 4.5 2829 11 8.0 4.1 2830 10.5 9.0 5.0 1.8831 11 8.0 4.8 1.5834 11 8.2 5.0 1.6835 11.5 8.0 5.5 1.5836 11.5 5.5 4.6 1.2837 11 9.0 6.5 1.4838 11.5 8.5 5.5 1.6839 10.5 8.0 5.5 1.5840 11.5 7.5 5.0 1.5

INVESTIGATION OF TEA DIODES WITH A DOPING NOTCH

2.1. Diodes with notch at the cathode

Extensive small-signal impedance measurements have been performed ondiodes of each of fourteen epitaxies with different doping profiles. It was ob- .served that there was a small dispersion of results within anyone epitaxy butthe results which will be presented in table II are considered typical of the epitaxywhich they represent. Table II presents the principal parameters of the epitaxies,

An example of the measured device impedance is shown in fig. 4. The deviceis taken from the epitaxy V 823. The negative of the device impedance (i.e.-Zd) is plotted on a positive Smith chart. The device is biased with 11.5 voltsand exhibits a negative resistance from 5.5-11.5 GHz. The evolution of thisdevices negative resistance at 7, 9 and 11 GHz as a function of applied biasis presented in fig. 5 which .also includes the development of the device impe-dance as the incident power is increased, for two different bias voltages (9.8 and11.5 volts). The manner in which the device impedance changes with increasingincident power is clearly a function of applied bias and takes the form predictedby the computer simulation.

Complementary small-signal measurements ~ich show the dependence ofbandwidth of negative resistance on applied bias are presented in fig. 6b whichshows the small-signal gain (into a 50 Q load) plotted against frequency. Theseresults indicate the tendency for both the negative resistance of the diode and

V=11.55VI=4.00mA

V823/Ta diode T

Fig. 4. Measured small-signal impedance as a function of frequency of a diode from theepitaxy V 823.

265


Fig. 5. Variation of small-signal impedance as a function of voltage at 7, 9 and 11 GHz aswell as large-signal measurements, for two bias values, at 11 GHz.

25~~-----------------------r~

'".!!!oc:

110

~----~----~~------~----~o11 13

- frequency (GHz)

-

Fig. 6. (a) Noise-figure measurements against frequency for different bias voltages (V 823).(b) Corresponding measurements of small-signal gain against frequency for different biasvoltages (V 823).


the value of the gain to decrease as the bias is increased. In addition there is ashift in the frequency of maximum gain towards lower frequencies as the biasis increased.

Measurements of noise figure which correspond to the measured values ofgain mentioned above are presented as fig. 6a. The noise figure exhibits aminimum for each value of applied bias. This minimum occurs at lower frequen-cies as the bias is increased. For frequencies less than 10 GHz increasing biasis accompanied by decreasing noise figure in accordance with an existingtheoretical model 13). The minimum measured value is 10.9 dB at 8 GHz foran applied bias of 17.0volts and the noise figure measured over a 4 GHz band-width from 7-11 GHz is 15.0 dB ± 1 dB for an applied bias of 11.55 volts.

Measurements of noise figure have been carried out on all the epitaxies at9 GHz under an 11.5 volts bias and the results are plotted in fig. 7b. Thisgraph gives an indication of the dependence of noise figure on r and con-sequently on the electric-field profile. The noise figure decreases from 21 dBto 14 dB as the value of I' increases from 1.4 to 3.4, indicating that smallernoise figures ensue from structures in which the field profile is most nearlyflat from cathode to anode 4). The device with smallest r value (I' = 1.2), cor-responding to the epitaxy V 836, gives a smaller noise figure as a result of itslower flat-region doping concentration rather than as a result of an effectrelated to r.The large-signal performance of all the epitaxies has been measured, in the

same 50 n coaxial mount, in order to compare the results with the computer

-... 4s x x'-- -_ xt- ~- --c: x - --.!!!:g 3 x - ..._.-... ....x..... ---lU ---I x -x-

x QJ:t7

2 23".:.s'J

21-EIU

19 .~c:

0

t17

-15

0, 131.5 2 3.5r{=N£/Nv}

Fig. 7. (a) Variation of amplifier efficiency, at 9 GHz, as a function of r. (b) Variation ofnoise figure (measured at 9 GHz) as a function of r.

268 J. MAGARSHACK. P. HARROP AND A. RABIER

Fig. 8. Large-signal measurements comparing two diodes of different r values with addedpower as parameter. Diode (a) (V 836) has an r value of 1.2 whilst diode (b) (V 823) hasan r value of 3.5.

predictions. A comparison has therefore been made of the large-signal impe-dance loops of two diodes which have r values at the extremes of the epitaxieswhich have been prepared. The result is shown in fig. 8.In general, this loop phenomenon represents an increase of the diodes negative

resistance as the input 'power is increased which occurs before the devicesaturates. This is probably due to r.f. excursions about the d.c. bias pointwhich tend to increase the average negative differential mobility.The d.c. power supplied to the two diodes whose characteristics are shown

in fig. 8 is about 3.7 watts in each case. Diode (a) corresponds to a diode fromthe series V 836 and diode (b) to a diode from the series V 823. It is appar-ent that the impedance loops of diode (a) are more closed than those presentedby diode (b) which is in broad agreement with the results of the computermodel. The parameters which are marked in the curves correspond to thevalues of added power at the maximum gain and at the maximum value ofadded power. The values of maximum added power for the two diodes at9 GHz (midband) are very similar which appears to contradiet the predictionsof the model, but it is necessary to point out that diode (a) has a flat-regiondoping profile (5.5X 1014 cm=") which is significantly lower than that of diode(b) (7.5x 1014 cm=") and would therefore be expected to be less efficient. Itmay be concluded, therefore, that despite its lower doping concentration diode


(a) is as efficient as diode (b) due to its shallower notch, which agrees with thegeneral trend of the computer predictions.With the exception of diode (a) all the devices have flat-region doping con-

centrations of about 8X 1014 cm-3 and so a comparison of their efficienciesisreasonably valid. This comparison forms the basis of fig. 7a where efficiencyat 9 GHz is plotted against r. The amplifier efficiency is defined as

Paj max 100%

0'

V IPol max

where Pal rnax = maximum value of added power,V = d.c. voltage across the diode,lpol max = d.c. current at maximum added power.

The efficiency in amplification is seen to increase from 2.5% to 3.7% as thevalue of r decreases from 3.4 to 1.5. There is therefore good agreement betweenthe trends predicted by the computer and the measurements.It should be pointed out that not all devices exhibited well-behaved saturation

characteristics and that some devices were subject to an abrupt change ofimpedance from small-signal to a point corresponding to a higher gain for thesame value of incident power. These devices were generally among those ofhighest efficiency.This phenomenon manifests itself as a "jump" in the amplifiertransfer characteristics and can be attributed to the form of the impedanceloop 14).

Some large-signal parameters of other epitaxies are summarised in table Ill,in which it can be seen that the epitaxy V 830 produced 212.6 mW of maximumadded power at 9 GHz with an efficiencyof 3.7%.The intermodulation performances of the devices have been measured by

injecting two equal-amplitude signals displaced in frequency by 5 MHz. Thepower in each of the frequencies f1' f2 at the input and at each of the frequen-cies f1' f2' 2f1 - f2 and 2f2 - f1 at the output was measured on a spectrumanalyser. Figure 9 shows intermodulation measurements on a diode from theepitaxy V 823 at 9.5 GHz. It is interesting to note that the onset of gain ex-pansion occurs at the same value of incident power which produces a non-linearity on the third-order intermodulation curve. The large-signal behaviourof this device was simulated and the third-order intermodulation product(LM.P.) was calculated as described in the previous section. The results of thiscalculation are shown in fig. 9, from which it can be seen that the modelpredicts a larger expansion of gain than measured in practice but that thereis excellent agreement between the calculated value of I.M.P. intercept pointof 15.8 dBm and measured value of 14.3 dBm.Measurements of LM.P. have been performed on this device, under identical

bias conditions, in two circuits of different characteristic impedances namely

TABLE III

Comparative performances of diodes with different notch depths

diode NF bias conditions bandwidth noise figure max. efficiency intermodula- noise in oscilla-serial no.

r=- addedpower ti on product tion 10 kHzNN(at 9 GHz) (at 9 GHz) (at 9 GHz) intercept point from carrier

(GHz) (dB) (mW) co (dBm) (Hzrms/lOOHz)

836 1.2

~

11.55 V 6.4-13.4 17.6 35.2 2.5 20.3 26385 mA

838 1.6 ~ 11.55 V 6.1-11.0 18.2 172.0 3.5 19.5442 mA

830 1.8

~

11.55 V 5.1-11.6 18.0 212.6 3.7 19.6530 mA

826 2.0.~

11.54 V 5.5-10.5 18.3 138.4 3.1 17.0435 mA

823/4 3.5

~

11.55 V 5.0-11.5 13.6 92.7 2.6 15.5 160320 mA

823/1 3.5 ~- 16 V 6.1-12.8 17.2 81.0 12.5 19.5-445 mA

(i.e. notchat anode)

tvCl

~

I'"~~~»-

~~e?>

~til~

271-------------------------------------------------------

PaT~10


30

a

-10

-20

-30

-40

-sa

-30 -10 a 10 20-F}n(d8m)

Fig. 9. Comparison between experimental and theoretically deduced curves of linearity and3rd-order I.M.P. at 9.5 GHz. Power values correspond to the power measured at each ofthe frequencies 11>12, 2/2 - 11 and 2/1 - 12' Here 12 - 11 = 5 MHz.

50 Q and 30 Q. The results are shown in fig. 10. The degree of gain expansionmeasured into 30 Q is very much larger than that measured into 50 Q and thecorresponding departure from linearity on the third-order I.M.P. is morepronounced for the 30 Q measurements. Furthermore the I.M.P. interceptpoint for the 30 Q case is +10.0 dBm compared with + 14.3 dBm for the50 Q measurements which confirms that it would be prudent to use a low-gainfinal stage in a chain of reflection amplifiers in order to improve the overallI.M.P. performance.Table III summarises the I.M.P. performance of some other epitaxies. The

best performance was offered by the series V 836 which produces an I.M.P.intercept point, without gain optimization, of +20.3 dBm for a small-signalgain of 9.5 dB into a 50 Q load.


o 10 20-l7n(dBm)

. Fig. 10. Linearity and 3rd-order I.M.P. measurements (diode V 823) in circuits of 50 and30 !l.

V=115VI=320mA

20 Tr823-4Po

(dBm)t 10

o

+14.3dBm

-10

-20

-50.11--30,[1

-50

-40 -10

2.2. Diode with notch at the anode

The following measurements were performed on the same devices biased suchthat the notch appeared at the anode.The results of small-signal impedance measurements are shown in fig. 11 for

bias conditions of 16 volts and 430 mA. This device (V 823) exhibits negativeresistance, under these d.c, conditions, from 6.1 to 12.8 GHz. Additional dataon the dependence of the bandwidth of negative resistance on bias conditionsis plotted in fig. 12b which indicates that near-octave bandwidths of negativeresistance can be obtained for bias voltages ranging from 12 volts to 18 volts.The centre frequency (approximately the frequency of maximum gain) occursat lower frequencies as the bias is increased. (The opposite dependence wasobserved for cathode-notch diodes.)The noise figure (fig. 12a) is generally 3 to 4 dB larger for this polarisation

than for the cathode-notch case. However, a noise figure of 18.0 dB ± 1.5 dBcan be obtained (V = 16.0 volts) which is associated with reasonable gain overthe frequency range 7-11 GHz.


V=16V[;:432mA V823/3 dIode 1

273

Fig. 11. Small-signal impedance measurements of a diode (V 823) biased so that the notchappears at the anode, as well as large-signal measurements at 7, 9 and 11 GHz with addedpower as parameter.

ëO ~---------------------------------------,~

lIJ.~oc:

113V14.V

15V

16V

10

7.5ëO~.s

5 g,

2.5!

Fig. 12. (a) Noise-figure variation with frequency for different values of applied bias (diodeV 823). Notch at the anode. (b) Corresponding values of small-signal gain.


Before describing the large-signal results it is worth noting that the devicesare not thermally optimized to operate in this sense and that the thermalresistance is larger when the notch is at the anode. Despite this fact, however,the results are very interesting.

Large-signal impedance measurements are shown in fig. 11 at 7, 9 and11 GHz where the parameter on the curves is maximum added power. It isclear by inspection of the figure that there is no loop phenomenon and there-fore no gain expansion whatsoever under these conditions. The low efficiencyof 1% which is measured at 9 GHz can be considered to be due to the lowvalue of effective nZ-product since the high-field region of this device is centredon the low-doped notch region. The disagreement which exists between thecomputer model and measurements may well have its origin in the non-equiv-alent thermal conditions.A comparison of the intermodulation performances has been made in figs 13

and 14 for a diode from the epitaxy V 823 biased with the notch at the cathodeand the notch at the anode respectively. In order to effect a meaningful com-parison, the small-signal gains have been chosen equal in the two cases. TheI.M.P. intercept points are + 14.5 dBm and + 19.5 dBm respectively. The com-

-30 -20 0 la 20--_ fin (dBm)

Fig. 13. Linearity and 3rd-order I.M.P. (diode V 823) at 9 GHz. Notch at the cathode.

V=tt.55VI=322mA

I /+t4.5dBm-;f/

11III1II1

20 'Jl823-tPo

(dBm)

1to

0

-tO

-20

-40

-50·


-41)

V=-T6VI=-4.45mA

20 Jl823-TPo

(dBm)

i 10

0

-10

-50

-30. o TO 20-F}n(dBm)

Fig. 14. Linearity and 3rd-order I.M.P. (diode V 823) at 9 GHz. Notch at the anode.

parison reveals that an anode-notch structure may prove interesting for certainapplications where low intermodulation products are of prime importance.Figure 15 shows a similar characteristic for a diode from another epitaxy(V 836) which gives rise to an I.M.P. intercept point of +25.0 dBm with anassociated small-signal gain of 4 dB.

Conclusions

Ithas been shown that a noise figure of 15 dB ± 1dB is possible in a 4 GHzbandwidth from 7-11 GHz and that a noise figure of 11 dB can be obtainedin a narrow bandwidth. This performance was obtained from a device with a, deep cathode notch. The results on several epitaxies of different doping profilesshow that shallow notch devices have larger noise figures as a result of anelectric-field distribution which departs from the constant profile desirable forlow noise figure.Large-signal impedance loops have been encountered for cathode-notch

diodes, both theoretically and experimentally, which, for conditions of equald.c. power, are more closed when the notch is shallow. This may be interestingin the design of broadband linear amplifiers.

L_ ~~_~ ...


-Ia

-20

-30

-,40

V=-16VI =-355mA +25dBm-//

//,/ .t

/ 1/ ,,

11111

20 Jl836/3

Fig. IS. Linearity and 3rd-order I.M.P. at 9 GHz of V 836 diode. Notch at the anode.

la 20--"fin (dBm)

-20 -Ia o

Experimental and theoretical evidence has been presented which indicatesthat shallow notch devices have higher efficiencies than deep notch devices.The required doping profile for low noise is thus incompatible with that requiredfor high efficiency.Devices have been produced which are capable of producing more than

200 mW maximum added power.It has been demonstrated that reversing the polarity of a diode such that

the notch appears at the anode, may result in improved intermodulation per-formance and under these, conditions an intermodulation intercept point of+25.0 dBm has been obtained.This study has demonstrated the feasibility of wideband medium-power

reflection amplifiers using Gunn diodes. It is reasonable to expect that deviceswith similar characteristics can be produced which would be used in amplifiersup to frequencies around 40 GHz.

Laboratoires d' Electroniqueet de Physique appliquée

Limeil-Brévannes, March 1976


REFERENCES1) R. CharIton, V. R. Freeman and G. S. Hobson, Electron. Lett, 7,575,1971.2) R. Spitalnik, M. P. Shaw, A. Rabier and J. Magarshack, Appl, Phys, Lett. 22,

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paper B.42.

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INVESTIGATION OF TRANSFERRED-ELECTRON AMPLIFIER DIODES ... Bound... · INVESTIGATION OF TRANSFERRED-ELECTRON AMPLIFIER DIODES WITH A ... mental study of Gunn diodes which have