SU1123069A1 - Photodetector for visible light region - Google Patents

Description

The invention relates to converters of light energy into electrical energy, in particular to photodetectors used in photometric measurement of light radiation and in film photographic technology.

For photometry and K1 2, photographic equipment is needed. Photoreceivers with a spectral characteristic close to the visibility curve of the human eye, i.e. with 1 maximum. sensitivity on. yellow-eulennoe region 2.1-2.4 eV, with a smooth with a decay of sensitivity to the edges of the visible range to able to work in a wide range of illumination, including a very small order

 . :.

A known receiver on the region: visible light, made on the basis of solid D1-.1X solutions of GaAsf, c-P). (x -0.32-0.52) or Ga.AlxAs (, 30, 68) with pn-junction in a solid solution. The advantage of a photodetector is the low threshold of sensitivity to weak light fluxes due to a small dark current due to the large band gap of solid solutions (1.72, 0 eV) 1..

The disadvantage of the photodetector is a sharply asymmetric spectrum of the photosensitive device with a steep low-energy and low-lying high-energy edge and the location of the maximum sensitivity in the red region of the spectrum 1.8-1.9 eV. Obtaining the spectrum of the phototream f close to the curve of the visibility of the eye. Upper is inefficient due to a decrease in quantum sensitivity as a result; large surface recombination and dark current increase ..

The closest technical solution to the invention is a photodetector to the visible region of light based on Ga. structures that contain a graded-gap narrow-gap slr with a p-G) -transition with a threshold energy value of p.p g / 1st forks in the p-region: n -transition of 1.7-1.9 eV, wide-gap layer (, 7) and energy gradient of direct transitions of a graded-gap layer directed from the wide-gap layer I.

The use of the varied structure and the shrkrzonny SLR on the illuminated surface makes it possible to eliminate surface recombination from the indicated irregular layer and to obtain a high photo sensitivity.

However, for such a photo-receiver (vEo) 120-130 EW./ SG4 (1 hx i mole О μm), with etrm in the spectrum of photo-sensitization (photosensitivity) there is

unchanged photosensitivity in the photon energy range h-5 2.02, 3 eV, i.e. There is no localization of the maximum in the spectrum and the steepness of the low-energy slope turns out to be significantly larger than what is required for photo receivers in the visible range. Such a spectral characteristic is obtained because with a table of small v EO, the semiconductor behaves almost like a homozone one.

The inconsistency of the photoresponder's photoresponder spectrum with an eye-visible curve leads to errors in the photometry of the light fluxes and in the exposure of objects of film-making equipment.

The aim of the invention is to obtain a spectrum of a photodetector close to the curve of visibility of the eye, while reducing the high quantum efficiency.

This goal is achieved by the fact that a photodetector in the visible region of light based on Ga (.xAl ;; Azstructure, containing a variable narrow-band layer with a pn-junction with the value of the direct energy of direct transitions in the region of the pn-junction 1.7- 1.9 eV, a wide-gap layer (x 0.1) with a gradient of energy of direct transitions vE of a graded-gap layer directed from the wide-gap layer, VEp removes the condition

 ..) fot. and uEg. (1)

and the shirkrozonny layer has a thickness b satisfying the condition

-one (

L 6 b S about.

where y is the reverse slope of the absorption edge in the narrow zone; oi-o is the absorption coefficient for direct transitions in a narrow zone;

4Ex is the interval of variation of the width of the forbidden zone in Oa .. As when v is varied from O to 1, the diffusion length of the nsrns of the xRRTells in the wider layer; "I, g - coefficient of prglrscheni on

right in the shyrokoernnrm layer at an energy of the frth equal to the progressed energy of the direct interflux. In this design of the receiver, the limitation of low-energy sensitivity to the edge of the visible range is achieved by choosing a direct energy source, which coincides with Eg for a normal zone, from dipairn 1.7-1.95 eV. The required steepness of the low-energy edge is determined by the magnitude of the energy gradient of the direct transitions vEg in the vari-anion layer. The shift of the maximum of sensitivity to the yellow-green region is achieved by decreasing the contribution of low-energy photons in the virtual layer. For low-energy photons, in the case when the volume radius of the aa r-row W is greater than the length of the photopath in the region of strong absorption, the path length is limited and is approximately Jiizlsfi. where EOO is the minimum energy of transitions to the heterointerfaces between the graded-gap and wide-band layers. Dependence of the density of the photocurrent I on the photon energy h-, i.e. The spectral characteristic in the low-energy region, provided that all electron-pair pairs are separated by a pn-junction, is represented as; -, 1.bF, () () (3 where photon flux density; g is electron charge. Low-energy steepness the edge of the spectrum at values of the 3JccnoHeHTbi index of less than one is approximately d. {- i-) ac-o (4) gh9 IvEol and decreases with increasing f,). A narrow-gap graded-gap layer is impractical as with smaller vEuJ than satisfying the condition (since the edge steepness will be as large as that of the known (otpriemnika), and with larger 1 because of the decrease in quantum photosensitivity due to the impossibility of complete absorption of photons pry small thickness of the narrow-band at | vE (.,,, In particular, if the value ot ,, is taken, which can vary within certain limits depending on the composition and doping level of the solid solution, equal to 10 cm, then the boundary conditions for L / U will be by an ejection of 100 eV / cm. | hOo} 6,700 eV / cm. The chosen direction of the energy gradient of direct transitions provides an increase in the collection rate of minority pn-junction carriers with increasing photon energy, as well as to the narrow-gap boundary of the graded-gap layer. This leads to a high quantum photosensitivity, is highly energetic to photons, and makes it possible, together with the parameters of the wide-gap layer, to control the position of the maximum sensitivity. The slope of the high-energy edge in the spectral characteristic of the photo- and receiver is determined by the choice of the thickness of the wide-gap layer within L 6 b ° C. x b c this non-photoactive absorption is not so great as to reduce the sensitivity of 4 receivers in visible area asti. The advantage of the thick layer is the ability to strictly set the steepness of the high-energy edge of the laser and the position of the maximum by choosing the direct energy Epe nets of Egg and thickness b i. Photographic absorption in the wide-gap laboratory samples of the proposed photodetectors is provided by choosing the thickness of this layer within 26 microns, which is greater than L, but less than the absorption length at the non-resonant transitions Lg j,, i.e. The theoretical calculation of the Fbto response spectrum of the proposed photodetector is based on a change in the absorption coefficient in Reason layer. The main points of the calculation model are: the region of collection of minority carriers is located in the ucozone part, the width of the region of collection qi is no reflection from the surface; the probability of collecting in the region is equal to one, and beyond its limits is zero. The expression for the photocurrent in different parts of the spectrum has the form h 5Е, Г g Еос «b бЕ„, -pKiA- l i r-4-ШEoa b; sEj e (.. h (Eow-Elv) h-Edv) f. i ". . -2G -

O. V-LY-EAV)

R

I: NEc.v ceov lv

.

I E, xZ | 00 (

L.E.C.

{.-E

g

. oi vc

t

zhb

Ll toftt4l fcoe

de oi is the photocurrent density;

% - photon flux density;

cio is the absorption coefficient and zone tails;

B is a constant that is included in the expression for the coefficient of the Gloss at B-Yr;

OO

: 0a

the threshold energies of direct transitions in the narrow-gap layer at the heterojunction with the wide, zone-layer and at a distance of oSod, respectively, osdc-absorption coefficients at the transitions in the narrow-gap and wide-gap layers, respectively ;. ; oigQjOigg are the rates of change in the absorption coefficients and Ы-or with increasing photon energy h;.

a, g is the absorption coefficient in a wide layer on indirect transitions at an energy equal to the energy of direct perisodes in it.

The following are the calculated spectra obtained for different values of (CHGE / O) and the following values of the design parameters 1.10)

.1.0-2. eV,

00 -118,

 10 cm-l00, cioe 5, 4 .10 cm,

01 1.21 (J cm,

., 5b eV, E ,, in

 2.00. EV (x 0.8) 3 microns, e.

 10cm-

The effect of eHUs the position of the maximum sensitivity and the steepness of the low-energy layer of the spectrum is unambiguous - the slope decreases with increasing l-vSpf, and the maximum of the sensitivity shifts towards large h4; and at I vEo) greater than 100-150 eV / cm, there is a yellow-green region of 2.1-2.4 eV.

Figure 1 shows the spectral characteristic of the proposed varistor-gap photodetector (1) and the eye visibility curve (2) in figure 2 — the structure of the tour of the proposed photo-receiver, illuminated by the light flux Fd; figure 3 - coordinate change. the threshold energy of direct transitions EO (continuous curve) and the width of the forbidden line Eg. (dash-dotted line) in the photo-receiver V in Fig. 4. - Theoretical photocurrent spectra of the photo of a rimon at different, eV / cm 2-200, 3-800 4-1300.

. This: photodetector (figure 2) is a heterostructure with a WAN

Reasoned narrow-gap layer 3 ,. containing the transition, and the wide-gap layer 4, adjacent to the narrow-gap aarizon band. A part of the surface of the tfflipOKO3OHHoro layer is covered with a contact layer 5 of GaAs. Layers 3-5 epitaxially deposited On the substrate 6 of CALZ on K the substrate and the contact layer are made of ohmic metal contacts 7 and 8.

The photodetector works as follows.

On the part of the photodetector uncovered by the contact layer, the luminous flux from the object being exposed falls

5 from the light source. In the graded-gap layer 3 (lig.2 and 3) of the photodetector, an electrical signal is generated that is proportional to the illumination of the object or the luminosity of the radiation source. The photodetector detects radiation in the visible range — with a maximum sensitivity in the yellow-green region 2.1. 2.4 eV and a sensitivity distribution proportional to the eye visibility curve. The generated electrical signal is removed from the ohmic contacts 7 and 8 and is used to control the mechanism for exposing the film photographic material or to measure the light fluxes of different personal intensity.

Figure 1 shows the spectral characteristic of a photodetector with the following parameters: Eg-Е ,, at the beginning and at the end of the growth of a graded-gap Gai. respectively equal to. 1.90 and 1.77 eV. The magnitude of the gradient is Erf or чЕ,.,, Defined as the difference Eg- at the beginning and at the end of the growth of a graded-gap

0 layers related to the thickness of this

layer is 360-405 eV / cm. The thickness of the wide-gap layer of 3 microns, and ve. X is 0.8-0.9 in it. The concentration of donors and acceptors is chosen

5 within (about, 7-5u.101 from the condition of equality of tunnel and darkish due to the generation of carriers in the layer of volume charge of the currents. The choice of concentration in the specified limits ensures the minimum threshold of photosensitivity 10 lx. The collection factor in the maximum of the created photodetectors is em 0.8 to photons with an energy of 2,18 eV, the average steepness of low-energy

spectrum edge 5 eV.

In the base object, a silicon photodetector is adopted with a light filter, cut off and an infrared region, which is currently used as a photoreceiver in the latest camera cameras. Compared with the base object, the proposed photoreceiver has the following advantages; Not no- ; required in the light filter, a low tempo saturation current of 10 A / mm due to the large size of the band gap in the p – 7 junction region (for silicon K 1.1 eV), the dark saturation current L / rviM, a low photosensitivity threshold 01--, a high quantum efficiency - up to 0.8 at the maximum. The proposed photodetector can be used in photometry of optical radiation and as a photodetector in cinematographic equipment and in exposure meters.

Claims (1)

PHOTO RECEIVER ON THE VISIBLE AREA OF LIGHT based on Ga ₁ . _to A1 _x As of the structure containing a graded-gap narrow-gap layer with a p - “transition with the threshold energy of direct transitions to the region of the“ - transition of 1.71.9 eV, a wide-gap layer (x> 0.1) with an energy gradient of direct transitions • УЕ _{0 of the} graded-gap layer, directed away from the wide-gap layer, with the fact that, in order to obtain a photodetector spectrum close to the curve of the eye, while maintaining high quantum efficiency, VE _O satisfies the condition X <* of ^E o1 <bEe ^ o "and the wide-gap layer has a thickness! Satisfying the condition where] f is the inverse steepness of the absorption edge in the narrow-eon layer; - absorption coefficient at direct transitions in a narrow-gap layer; & En is the interval of variation of the width of the forbidden zone in Ga <. _x Al _x As when changing X from 0 to 1; L is the diffusion length of minority carriers in the wide-gap layer; '' is the absorption coefficient at indirect transitions in a wide-gap layer at a photon energy equal to the threshold energy of direct transitions.