Note: Descriptions are shown in the official language in which they were submitted.
-
~ 17~4~8
MET~()D /~):F R}~CTIF~II\TG ALq'~N ATI~G
CURRE~ All~) APPARA~I~US E`()E~ PERFO~
1~ G 'l`E[IS I~E ' C rTO D
The present inven-tion relates to electrical engi-
neerin~ ancl semiconduc-tor devices, and more particularly
it relates to methods o~ recti~ying al-ternatinF; curren-t
an(l ~o apparatus capable of performing such methods~
~ he most advantageous ~ield o~ aPplications of the
present invention is the provision o~ recti~iers for pow-
er transmission.
For the purposes o~ convertin~, trans~rming and
transmitting electric power o~ high power values over con-
siderable distances there are required nowadays recti~i-
ers capable o~ handling high voltages and ~reat current
values. The industrially used diode or uncontrolled pow-
er rec-tifiers and -th~ristors are limi-ted by the dimensions
o~ the rectifying layers and the technology o~ t~eir fab-
rication. It is there~ore desirable -to develop principal-
ly novel recti~ier units and methods not based on a tech-
nologically built-in recti~ying layer.
Known in the art are methods of recti~ying alter-
nating current with aid o~ semiconductor diodes of vari-
ous types, includin~ technologically built-in rectifying
layers (cf. "The Fundamentals o~ Physics o~ Semiconduc-
tor Devices" by Y.A. ~edo-tov; in Russian, Moscow1 "Soviet-
skoe Radio" Publishers, 1970, pp. 1~8-139).
The known semiconductor or solici-state diodes are
175~7
-- 2--
rectifying elements comprising a recti~ying layer tech-
nologicall~ built-in either witLin tlle body or on the
su~face o~ tf.e serrllcon~uctor, having -two electric leads
and an appropriate construction.
The small -thickness and insu~icient tecllnical ho-
~llogeneity o~ the rec-tifying layer have been ~ound to a~-
fect its electric stren~jth. On account of this, -the known
devices would not withstand higrl voltages and great cur-
ren-t density values. The theore-tical limit oi current
density in case of germanium and silico~iodes with a
recti~ying layer is assessed as 106 A/m2, which, however,
would not be attained in practical cases. Furthermore,
-the necessit~ oP using technologies of providing a recti-
fying layer either within the body or o~khe surface o~
a semiconductor both complicates and rises the co~t of
manufacture o~ alternating-current rectifiers.
~ nown in the art is a met~od o~ recti~ying elect-
ric current in a semiconductor without a -technologically
built-in rectifying layer. This method is based on creat-
ing a concentration gradient in a semiconductor with aid
o~ a temperature g~radient (c~. "Photo- and ~hermoelectric
Phenomena in Semiconductors" by J. Tauts; Russian -trans-
lation, Moscow, "~oreign Literature" Publishers, 1962,
p ~
Accordin~ to the known method, a temperature gradi-
ent is induced in a homo~eneous e~trinsic or impurity semi-
oonduc-tor by means of a heater and a cooler arranged at
1 175'L78
--3--
the opposi-te ends of a specimen, so as -to ensure a gra-
dien-t of the concentration of the majority current car-
riers. With this tempera-ture graclient being su~ficient-
ly sharp, so that the concen-tration o~ the majority cur~
rent carriers significa~l-tly varies over the diffusion
bias length, non-equilibrium current carriers appear, and
the curren-t is rec-tified.
However, this known method o~ recti~yin~ alternat-
in~ current is characterized by a 10W efficiency fac~tor
on account of the low recti~ication ~actor. For this rea-
son the method has failed to fi~d practical applications.
A hi~her efficiency factor is o~ered b~ another
known method o~ rectifying alter~ating current (c~ et-
ter3 of Journal of Technical Physics~' by Kh.I. Amirkha-
nov, E.~. Aliev, R.I~ Bashirov, ~.~1. Gadzhialiev, Vol. 4,
p. 660, 1978~. According to the known method, a heater
and a cooler arranged at the opposite ends of a germanium
wa~er are used to provide a gradient of the ratio of the
mobilities of electrons and holes longitudinally of the
wa~er, thus creating a tel~perature gradient and bipolar
conduction by heating one end of the g~ermanium wafe~ and
cooling its opposite end. '~he bipolar conduction is ensur-
ed b~ the heater -temperature.
However, even this method which we consider -to be
the closest prior art OI' the presen-t invention is charac-
terized by a relatively low efficiency factor, on account,
~ - ~
~ 175~78
among other things, of energy consumption by the heater.
Furthermore, an apparatus for performing this method
is structurally complicated:by the necessity of matching the
heater to the semiconductor, of providing heat insulation of
the heater, of having connection wires and a power source for
supplying the heater.
It is an object of the present inventiontoeliminate
the abovementioned disadvantages of 'he method and to broaden
the operational capabilities of the apparatus for performing
same.
According to the present invention there is provided
a method of rectifying alternating current by providing a
gradient of the ratio of the mobilities of electrones and holes
in a semiconductor with the aid of a temperature gradient,
wherein the temperature gradient and the bipolar conductivity
are provided by self-heating of the material of the semicon-
ductor by the current being rectified in combination with
cooling a part of the material of the semiconductor, the value
of the exponent of the power (a) of the temperature (T) de-
pendence of the ratio (b) of the mobilities of electrones and
holes (b ~ Ta) being not less than 0.1.
'^':: ^
: .
~ 175478
The efficiency factor of the rectifying operation
is thus enhanced both by eliminating the energy consumption
by the heater and by the appearance of the square-law
characteristic of the relationship between the rectification
effect and the current density (the positive feedback rela-
tionship between rectification and the current density).
~he range of semiconductor materials usable for rectification
has been also broadened.
Furthermore, the object of the invention is attained
in an apparatus for performing the above-specified method,
comprising a semiconductor working element with non-rectifying
contacts and a cooler adjoining the working element, in which
apparatus, in accordance with the invention, the dimensions
of the working element are selected to ensure, in combination
with the action of the cooler within the range of the working
currents, non-uniform self-heating by the current being
rectified, with the gradient of the ratio of the mobilities of
electrons and holes ( db ) not less than 0.2 cm 1, and bipolar
conduction of the working element.
The invention simplifies the structure of the recti-
fier and makes it less costly, owing to the elimination
~ - 5 -
~ ~ 75~78
v:e the heater.
To ~roaden the operational ab.ilities of the appara-
tus 9 i t iS e~pedient -to have the cooler movable longi-tu-
dinally OI' the -working elemerlt.
This enables to solve a number of technical problems
associa-ted wit.l rectiLication by con-trolling -the volt-am-
pere chaLacteristic with aid OI displacing the cooler.
The invention will be further described in connec-
tion witll e~lbodimen-ts thereoI, with re~erence beingJ had
to the accompanJing drawings, wherein:
FIG. 1 illustrates sche~latically an apparatus eor
per~oIming the method ol recti~ying electric current in
accordanca with -the invention;
FIG. ~ is a circuit diagram of wiring the apparatus
into an ~-lectric circuit, with hal~-wave recti~ication;
FIG. 3 is a modi~ication Oe the aPparatus ~or per~
~orming the ~ethod Oe recti~ying alternating current in ac-
cordance with the invention;
FIG. 4 is a circuit diagram O~e wiring the apparatus
into an electric circuit, with full-wave recti~ication;
~ IG. 5 is another modifica-tion of the apparatus ~or
performing the method Oe rectifying alternating current
in accordance with ttle inven-tion;
FIGo 6 is the apparatus shown in FIG. 5, with addi-
tional contacts.
Re~erring now to the drawings, -the apparatus 1 ~or
rectif~ing alternatin,, current, according to the invention,
compriseS a workin~, element 2 (FIG. 1) made oI~ a semicon-
1 17~478
--7--
ductor wi-th different -temperat~e der)endences of trhe rno-
bility ol el ctrons and holts. The two opposite end faces
o:f -tne working elemerlt 2 have connected thereto non-rect
ifyin~ con-tac-ts 3 and 4 by which the a-,opara-tus 1 is con-
nectable to an electric circuitO The end of' -the worhing
element 2 provided ~-rith the contact 4 is adjoined by a
cooler 5 which is ei-ther air- or water-cooled.
The dimensions of -the working element are selected
in accordance with the loss inde~ ( Nl ~ of the rec-ti~ied
current in the wor-king element 2, to provide the highest
possible temperature gradient; Nl = IlVl wherein Il is
tile current through the working element 2 and Vl is the
voltage drop ac.ross the working element 2.
By ~irst a~proxima-tion, the dimensions of the work-
ing element 2 can be compu-ted from the formula:
s = T1 ~1 e
herein ~e is the heat conductivity factor of the mate-
rial of' the working element 2;
T is the ternperature differential between the
ends of the working elements 2 at the con-
tacts 3 and 4;
1 is the length of the working element 2;
S is the cross-sec-tional area of the working
element 2.
- .~
1 ~7547~
AccordinP -to t;~ie irlvention7 t;le value of the tem-
perature ,radient ~I^ovl(l be at least 0-2~ '1' , where-
in '~ iS the temperature, ~, arld "b" is -the ratio of the
rnobilities o~ -the elec-trons and holes. In practical appli-
ca-tions, it i6 expedient -to a-ttain the highest tempera-
ture gradient possible, so as to step up the ef~iciency
factor. ~he cooler ifi e~pected -to provide the ma~imum
withdrawal ol the heat dissipated in -the working element 2.
In opera-tion, the apparatus 1 is wired into an al-
-ternating-current circuit ~ . 2) in series wi-th a load
6 and a resistor 7 -through a control transformer 8. '~he
required value o~ -the rectified voltage is preset Wit~l
the trans~ormer 8, and the requi1ed current value is pre-
set with -the resistor 7. With the workin~ current and volt-
age range at-tained and the cooler 5 turned on, the work-
in~ element 2 (FIG. 1) heats up. The temperature of the
hot portion of the working element 2 provides for bipolar
(in-trinsic) conduction, with at least a part OI the volume
of the therrnally non-uniform workin~ elemen-t 2 displaying
this bipolar conduction, i.e. beinK filled with electrons
and holes within a tempera-ture field. As the working ele-
ment 2 is made of a material wi-th di~ferent temperature
de~endences OI the mobilities of electrons and holes,
there is set within trLe working element 2 alongside of
the temperatllre gradien-t a gradient of the ratio ( d~
o~ t-he rnobilities of electrons and holes:
1 17547~
b = b('~ T~ _ = c T
~lerein ~e is the mobility OI' electrons~
p is the mobili-ty o~ holes,
c is a num~;rical coe~ficient.
'I'his results in variation of the injection ( ~ )
factor lorjnitudinally o~ the working element 2, alongside
oL the temperature gradient:
(X ) = -
1 ~ p~ xherein n is the concentration of elec-trons J
p is -the concentration of holes.
~ or the area o~ intrinsic conduction, the injection
factor is:
k, (X ) 1 _
1~ g~X)
With the current flowing through -the portions of
the workin, element 2 with different values o~ the in-
jection factor ( ~ ), non-equilibrium current carriers
are either injected or e~tracted i~ accordance with the
relative direc-tions of the temperature gradient ( dT
and c ~ rent density (j).
In case oi intrinsic conduction, the concentration
o~ non-equilibrium holes (~ p ) is deter~Qined by the gra-
dient o~ the ratio of the mobilities and the current den~
1 17547d
-10-
~i~y
~ /) 2 ~ f
q is the charge o~ an electron;
is the lifetirne o~ non-equilibrium current
carriers~
j is the current densit~.
db
In -the method o~ the pIior art, dx is provided
by the temperature gradient, with aid of the heater and
the cooler. ~herefore, in the method o~ the prior art
there is a linear relationship between recti~icatio~ and
the current density.
In accordance with the invention, the gradient o~
the ratio of the mobilities ( db ) is provided by sel~
heating: _
@=c~g'~ = o~t
In ~irst apProximat;ion:
V
X ~
wherei~ V i9 the voltage drop across the working eleme~t
2. There~ore, in acc~rdarlce with the invention, there is
a square-law characteristic o~ the relationship between
the concentration of non-equilibrium current carriers (~ )
and the culrent density: , ~
/) T
1 17~478
wherein ~ is the exponent of the power of the te~-
perature dependence of the ratio of the
mobilities of the electrons and holes;
j is the current density;
V is the voltage drop across the working
element Z;
is the heat conductivity factor of the
material of the working element 2;
q is the charge of an electron;
T is the temperature, ~K;
T iS the lifetime of non-equilibrium current
carriers.
Designating ~ =~b the following is obtained:
T
ap= ~T _ (2)
Multiplying both sides of the equation by Mp-q(b+l),
one obtains:
~P ~p~q(b+l)=~lpq(~+l) j2 V ~ _
a~-q(b+1)2 (3)
The left-hand side of this equation is the specific
conductivity of the working element 2, due to non-
equilibrium current carriers, i.e. Qp;~p-q(b-~l)= a-aO
where a is the general conductivity of the working
element 2.
- j2v
Deslgnatlng ~ -~ ~hen a-aO=~. - (4)
Since a = jL, where L is the length of the working
element 2, a quadratic equation with respect to j is
obtained: 2 2
j V B -j + aO V = O (5)
~RL L
1 175~7~
The solution of that equation is
1 4 Q'B V
~-L
2B-V ~-L (6)
In the passing direction j > O, V> O.
It is evident from this equation that the max-
imum value of the voltage drop on the working element
2 is obtained when j has a single solution il at which
the apparatus is turned on and rectifies for all j ~ jl.
In order to find the value of Vl it should be assumed
that:
r_ _
~ 4 ~-B V~3 = O
~Q.L2 (7)
from which V~ 1/3 (8)
4aO
Then, from equation 6, taking equation (7)
into account
j = _ L
2B~V12 (9)
Inserting the value of Vl from equation (8)
into equation (9), it follows that:
Ll/3S 1 ~( ~ ) 1/3 , ~O /3
(10)
where ~ is the heat conductivity factor of the working
element 2,
~O is the specific intrinsic conduction of
the working element 2,
L is the length of the working element 2,
S is the area of the cross section of the
working element 2,
-b
(b+l)-T
¦~ - lla -
-` I 175d~
T iS the life time of the non-equ~librium cur-
rent carriers,
~ e,~p is the mobility of electrons and holes re-
spectively,
b-
~P
~ is the exponent in the relationship b (T ) ~T~,
T is the average temperature of the working
element 2, j= J
J is the intensity of the working current.
With the implementation of the disclosed solu-
tion of the problem, there is attained positive feedback
relationship between the current density and the concen-
tration of injected çurrent carriers, whereby the rectifi-
cation factor sharply rises, and the efficiency factor rises
accordingly.
Where the directions of thecurrent and tempera-
ture gradient coincide, there takes place injection ofnon-equilibrium current carriers from some portions of
the working element 2 into others; the re~istance of the
working
~ - llb -
l 1~5~78
-12~
element 2 drops, and the apl~aratus 1 (FlG. 2) is conduc-
-tive.
The direction oi t.he -temperature p,radient in the
worling element 2 (~IG. 1) does no-t depend on the cur-
ren-t alrection aad is deterrlined by -the arrangement of
the cooler 5 ralative -to -the end faces of the working ele-
men-t 2. 'f'here~lore, during the successive hal:e wave peIiod
the directions ol~ -the current and temperature gradient
become opposite; there takes place extraction o~ non-equi-
librium current carriers; the resistance O:e the working
element 2 rises, and the apparatus 1 curbs down the cur-
ren-t value.
It can be seen from -the above formula -that the value
oî ~ p determining the rectification process is dependent
on the parameter ~ . When selectinf^; -the semiconductor
material, i-t is expedient to chose the material with -the
hi~"hest possible value of ~ , with otherwise similar
values o:~ other parameters ( ~~, æ, ~ ). Thus, germanium
( ~ = 0.~7) is ~nore suitable than silicon ( ~ = 0.3).
Semiconductors with the value of ~ short of 0.1
in the apparatus in accordance with the invention render
it incompetitive wi-th known semiconductor diodes.
Let us consider embodiments of the aPParatU9 1 il-
lustrated in FIG. 2, comprising a germanium workinr element
2. In case of gerl.uanium, wi-th current dissipa-ted by tha
thermal oscillation oL -the cr~vstal lattice, the e~ponent
l 175~78
-J~3-
o~ the polier o the -tempera-ture de~endence oL' the mobi-
ll~y ratio ol' el~,ctrons and holes i9 0.67 ( ~ = 0.~7).
The worLini, element 2 was made oi? hole conduction
ger~aniu,illNith speci~ic resistarlce ~ = 40 Ohm.cm, sLiaped
into a rec-tangular wa~er with dimensions 2.0 x 1.0 ~
x 1.0 mm. 1~10rl-recti~ying contacts 3 and 4 were made by
in~usion oP indium-antimony alloy into the end ~aces of
-the workin~ element 2. The cooler 5 had a copper casing
and was water-cooled.
~ et us consi(ler examples oi' the per~ormance o~ the
abovespeci~ied embodiment o~7 -the appara-tus 1.
Example 1.
Wi-th working curren-t I = 0.02 A, the selec-ted dimen-
sions o~ the working element 2 provided, in combination
with -the operation o~ the cooler 5, non-uni~orm sel~-heat-
ing of the working element 2 with the value of the gradi-
ent ddb = 0.2. The e~iciency factor was ~ = 10%.
The power rating was -N = 1.5 W.
~ xample 2.
With workin~, current 1 = 0.5 A, the selected dimen-
sions o~' the working element 2 provided, in combination
with the operation o~ the cooler 5, non-uni~orm sel~-heat-
ing o~ the working element 2 with the value o~ the gradi-
ent ddb = 2Ø ~he e~iciency factor was 7 = 50 %.
'The power rating was N = 7 W.
~ 175478
_lLl,._
Exarnple 3.
With working current I = 1.0 A, -the selected dimen-
sions of' the working elemen-t 2 provided ? in combination
with the operation o~ the cooler 5, non-uniform self'-heat-
ing of .the working element 2 with the valu~, oI' the gradi
en-t ddb = 2.5. The e~f'iciency factor was ~ = 90 %.The
power ratinK was N = lGO W.
Exarnple 4.
With working current I = 4.0 A, the selec-ted dimen-
sions o~ the working element 2 provided, in combina-tion
wit~ the operation o~ the cvoler 5, non-unif'orm sel~-heat-
ing of the ~orking element 2 with the value of' -the gradi-
en-t ddb = 4.0~ Th~ ef'ficiency factor was ~ = 99%. The
power ratinf~ was N = 2 kW.
Let us consider an ernbodiment of' the apparatus 1 il-
lustrated in ~IG. 1 with the worLing element 2 made oi si-
licon. In case of' silicon the exponent of the power o~ the
temperature dependence of' the mobility ratio of' electrons
and holes is 0.3 ( ~ = 0.3).
The working elemen-t 2 was made of' hole conduction si-
licon with the specific resistance ~ = 1200 Ohm.cm, shap-
ed as a rectangular wafer with dimensions 4.0xl.0~1.0 mm.
~on-recti~ying contacts 3 and 4 were made by inf'using alu-
minium into the end f'aces of' the working element 2. The
working element 2 was soldered to -the cooler 5 witn aid o~
~, ,~ ,
--= ~
1 175~7~1
a speci~ic solder. T~e cooler 5 had a copper wa-teI-cooled
casing.
Let us consider e~amples of the performance o~ the
apparatus 1 ;Jith the si,licon working element 2.
hxalilp].e 1.
~ 'Jith working current I = 1.4 A, -the selected di-
mensions OL the workin~ element 2 provided in cornbi~ation
with t~le operation oi' the cooler 5, non-uni~orm sell'-heat-
in~ o~ the working, element 2 with -the value o~ the gradi-
ent db = 1.1. The e~iciency factor was ~ = 75 ~0. The
power ratin,~ was N = 500 K~.
Example 2.
~ ith working current I = 1.5 A, -the selected dimen-
sions o~ the working element 2 provided, in combination
with the operation o~ the cooler 5, non-uni~orm sel~-heat-
ing o~ the workin~ element 2 with -the value o~ the gradi-
ent -dd~ = 1.23. The e~ficiency f`actor was ~ = 78 %.
The power rating was N - 600 W.
Example 3.
l~ith working current I = 1.8 A, -the selected dimen-
sions of' the working elemen-t 2 in combina-tion with the
operation of' the cooler 5 provided self-hea-ting o~ the
vrorking element 2 with the value of` the gradient d- =
= 1.25. The ef'f'iciency f7actor was ~ = 82 % . The power
ratin~, was li = 650 W.
1 175~L78
--16--
Th~ apparatus 1 (l'IG. 1) wired in-to the circuit
illustrated in FIG. 2 passes c~rren-t durin~?; one half-wave
period~ i.e. per~orms hal~-v~ave recti~cation.
The use both h,llf-waves of alternatin~j c~ rent, there
can be emp]oyed a modi~ication 9 O:e the appara-tus, illust-
rated in FIG. 3, wired into the circui;t illustrated in
~'IG. 4. The ap~aratus ~ (FIG. 3) is a modi~ication oY t~le
apparatus 1 (FIG. 1), wherein the workin~ member 10 (FIG.3)
iS U-shaPed, with three non-rectieyirlr, contacts. The cold
contact 11 is connected to a central point o~ the trans-
~ormer 8 (FIG. 4). The hot contacts 12 and 13 (~IG. 3) are
connected to the terminal points o~ the trans~ormer 8
(FIG. 4). In -this modieica-tion, the apparatus 9 wired into
the circuit il]ustrated in FIG. 4 provides full-wave recti-
~ication o~" alternating current.
Let us con~ider an embodiment o~ the apparatus 9.
The wor'~in~ element 10 (FIG. 3) was made OI' hole conduc-
tion germanium wi-th speciI'ic resistance ~ = 40 Ohm.cm. The
two le~s O:e the U-shar~ed workin~ element 10 had the common
base. Theldimensions OI' each leg were 2.0 x 1,0 x 1.0 mm.
The base dimensions were 2.~ ~ 1.0 x 0.2 mm.
The working element 10 had three non-rectieying con-
tacts 11, 12 and 13 made by iniusion of' an indiu~-antimorly
alloy into the common end ~ace oiJ the working element 10
(contact 11) and into the end ~aces of both le~js ~contacts
12 and 13). The working element 10 was soldered to the
t7547
--17--
cooler 14 at the side o~ the common end face. I`he cooler
14 had a ~!ater-cooled copper casi.n~. The per~ormance o~
the apparatus 9 was p~actically -the same as that illus-t-
rated in the above e~amples O:e the per~ormance of the ap-
paratus 1 (FIG. 1) ~ith the working elernen-t 2 made o~ ger-
manium.
To extend -the operational capabilities oI' the appa-
ratus in accordance with the present invention, it is expe-
dien-t to raake the cooler 15 (FIG. 5) adjus-table longi-tu-
dinally of -the working element 16, to arrange a non-recti-
~ying con-tact 17 centrally of the worKin~ element 16 and
to provide non~rectifying contacts 18 and 19 at tne oppo-
site ends o~ the working element 16. I~ the cooler 15 is
adjusted to adjoin one of -t~e ends o- -the working element
16, the apparatus can be wired into a circuit via the con-
tacts 18 and 19, -to rectify al-terna-ting cur.rent similarly
to the apparatus 1 (FIG. 1).
With -the cooler 1~ adjusted centrally of the working
element 16, as it is shown in FIG. 5, the apparatus func-
tions as two apparatus 1 of the first~described embodiment,
connected in series in the non-conducting direction. With
this arrangement o~ tne cooler 15 the resistance o~ the
apparatus is at the maximum, and it curbs down the current
in the circui-t ~or either half-wave of tne alternating-
current voltage. I~, on t~le other hand, the contacts 18
and 19 (FIG. 6) are interconnected into a common lead, the
1 175478
wiring o~ the apparatus into a c~rent vie either the con-
tacts 17 and l& or tne contacts 17 and 19 would result in
the apparatlls ~)resenting the minirnurn resistance to al-ter-
nating current, since each hall~ o~ the apparatu~ would
pass one hal~-~ave o~ the al-ternating current voltage.
Let us consider an embodimen~t o~ the apparatus il-
lustrated in FIGS 5 and 6.
'~he -~orking elernent 16 was made o~ germanium with
specific resistance ~ = 40 Ohm.cm, shaDed as a cylinder
5 mm in diameter, 5 cm lor~. Non-recti~ying con-tacts 17,
18 and 19 o~ an indiurn-antimony alloy were in~used, res-
pectively, at -the centre and ends o~ the workin~ element
16.
The cooler 15 was made o~ copper ~or air-cooling,
~or adjustment longitudinally of the working element 16.
Int~mate contact o~ the cooler 15 with the body o~ -the
working element 16 was insured, ~vith the cooler being 5 mm
thick and having a ribbed e~ternal surface.
'~he implemen-tation o:E ~the disclosed solution o~ the
technical problet~ enables to step up the ef~iciency fac-tor
o~ rectifiers devoid o~ a technologicall~ built-in recti-
~ying layer, si~llpli~ies the struc-ture o~ semiconduc-tor
power rectiEiers and reduces -their costi it also enables
to recti~y hi~3her voltages and greater currents and to
control -the current value in a circuit.
