JPS59163878A - Semiconductor photo detector - Google Patents

Abstract

PURPOSE:To increase an ionization rate ratio of electrons to holes, and to reduce multiplication noises by forming a multiplication layer in an APD in superlattice structure. CONSTITUTION:Superlattice structure 12 in which N<-> type InP layers 12a and N<-> type In0.53Ga0.47As layers 12b are laminated alternately is formed onto a P<+> type InP substrate 11. An N<-> type In0.53Ga0.47As optical absorption layer 13 is formed while being in contact with the structure 12. A mesa type etching in depth reaching to the substrate 11 is executed. A non-reflection coating film 14 is formed on the surface of the layer 13. A surface protective film 15 is shaped to a mesa etching surface. The films 14, 15 are formed by Si3N4, etc. An N side electrode 16 is formed to the layer 13 by AuGe. A P side electrode 17 is shaped to the substrate 11 by AnZn. When holes generated in the layer 13 enter to the layers 12b from the layers 12a, the state in which apparently excessive energy is obtained only by the energy difference of valence bands is brought. The ionization rate of holes is increased, and an ionization rate ratio is augmented.

Description

[Detailed Description of the Invention] +a+ Technical Field of the Invention The present invention relates to a semiconductor light receiving device, and particularly to a light receiving wavelength of 1 [C] or more.
．． The present invention relates to an avalanche photodiode having a structure that is suitable for a band of 65 C μm or less and whose noise is reduced beyond physical limitations.

(1)) Technology background In optical communications and other systems that use light as a medium for information signals, semiconductor photodetectors that convert optical signals into electrical signals are one of the important and basic components, and many are already in use. has been made into Among these semiconductor light receiving devices, an avalanche photodiode (hereinafter abbreviated as APD), whose sensitivity is increased by multiplying the photocurrent by avalanche breakdown, is highly effective in improving the signal-to-noise ratio of a photodetector.

In optical fiber communication, which is a typical example of semiconductor photodetector applications, the material dispersion (based on the wavelength dependence of the refractive index) of silica (SRO2) optical fiber used for optical transmission is extremely high near the wavelength of 1.3 [μm]. The sum of material dispersion and structural dispersion (based on the wavelength dependence of the propagation constant), that is, intra-mode dispersion, is 1.3 to 1.55 Cμm at wavelength.
becomes smaller at .

Therefore, as a semiconductor photodetector for optical communication, the wavelength is 1 [μm].
There is a demand for an APD having excellent characteristics in the above band, particularly in the band of about 1.3 [μm] to 1.65 (μm).

(C1 Prior Art and Problems Many proposals have already been made using germanium (Ge) or TTT-V group compound semiconductors as APDs targeting a wavelength band of 1 [μm] or more.

■- Among the V group compound semiconductors, indium phosphorus (InP)
) Indium-gallium-arsenic (I) lattice-matched to the crystal
nGaAs) or indium, gallium, arsenic,
APDs using phosphorus (InGaAsP) mixed crystals have good light-receiving sensitivity in this wavelength band, and have physical properties such as lower noise and lower dark current than Ge, which is currently in practical use. It occupies an important position as a light receiving device that supports wavelength bands.

FIG. 1 is a sectional view showing a typical structure of an InP-InGaAs APD. In the figure, 1 is n++In
P substrate, 2 is n-type InP buffer layer, 3 is n-type InG
aA (s light absorption layer, 4 is n-type InP window layer, 5 is I
A p-type region formed in the nP window layer 4, 6 a p-type region constituting a guard ring, 7 a protective insulating film, 8 an antireflection film, 9 a p-side electrode, and 10 an n-side electrode.

By applying a reverse bias voltage to this APD, with the n-side electrode 10 being positive and the p-side electrode 9 being negative, p? A depletion layer is formed across the junction, that is, the interface between the p + -type region 5 and the n-type InP window layer 4, and this is an n-type InP layer.
s extends to the light absorption layer 3, and within this light absorption layer 3, electrons are excited to the conduction band by the input signal light,
Electron-hole pairs are generated, and the electrons are n(I'III electrode 10,
The holes drift toward the p-side electrode 9, and avalanche multiplication occurs in the n-type InP window layer 4 using the holes as primary carriers. For this reason, the n-type InP window layer 4 is also called a multiplication layer or a multiplication region.

In the process of avalanche multiplication, there is statistical fluctuation in the number of collisions between carriers and atoms constituting the crystal lattice, which causes inherent shot noise. This noise is usually called multiplication noise.

In the process of avalanche multiplication, when the number of times electrons undergo collision ionization per unit length, that is, the electron ionization rate is α and the hole ionization rate is β, the ionization rate ratio k (β/α or α/β) is When the ratio is close to 1, the multiplication noise is large, and when the ionization rate ratio is large, the multiplication noise decreases when the ratio is 3-.

In the conventional example of the I nP - I nGaAs APD described above, the ionization rate ratio = α/β is as small as about 2 to 3, and there are physical restrictions on the multiplication noise.

On the other hand, the introduction of superlattice structures has been proposed for various semiconductor devices, and for APDs, the multiplier layer is made of gallium arsenide (GaAs) and gallium Φ aluminum arsenide (G
As a superlattice structure in which layers (aAtAs ) are alternately stacked, the apparent ionization energy of carriers increases or decreases due to the discontinuity in the energy band that occurs at the heterojunction interface between the GaAs layers and the GaAtAs layers, and electrons and positive Structures that reduce multiplication noise by increasing the ionization rate ratio with holes are already known.

However, depending on the GaAs-GaAtAs-based semiconductor material, it is impossible to construct a light receiving device that supports a wavelength band of 1.0 [μm] or more.
There is a demand for an APD structure that uses AsP-based semiconductor materials and that exceeds the physical limitations described above.

4- +d+ Purpose of the Invention The present invention provides a wavelength range of 1 [μm] or more, particularly a wavelength of 1.3 [μm] or more.
It is an object of the present invention to provide an avalanche photodiode that is compatible with the band from [μm] to 1.65 [μm] and has extremely low noise.

(61 Structure of the Invention The object of the present invention is to provide an indium-phosphorus compound semiconductor substrate, and a semiconductor made of an indium-gallium-arsenic compound or an indium-gallium-arsenic-phosphorus compound formed by lattice matching with the crystal of the substrate. It includes a light absorption region and an avalanche multiplication region having a superlattice structure in which indium-phosphorus compound semiconductor layers and semiconductor layers made of an indium-gallium-arsenic compound or an indium-gallium-arsenic-phosphorus compound are alternately stacked. This is achieved by a semiconductor light receiving device that has a 300-degree turn.

In particular, the thickness of the indium phosphorus compound semiconductor layer and the semiconductor layer made of an indium-gallium-arsenic compound or an indium-gallium-arsenic-phosphorus compound constituting a superlattice structure is 30 (nm) or more and 70 (nm) or less, and the superlattice structure is The most significant deafening effect can be obtained when the total thickness is 0.5 (μm) or more.

(f) Embodiments of the Invention The present invention will be specifically described below by way of embodiments with reference to the drawings.

FIGS. 2(a) and 2(b) are cross-sectional views showing the main manufacturing steps of an embodiment of the present invention.

Figure 2 ial reference impurity concentration is moderately higher than I
Above, the impurity concentration is I x 10'' [crn-3
J or less, the +11p layer 12a and the n-type indium-gallium-arsenic compound (In053Qao, 47
A superlattice structure 12 in which As) layers 12b are alternately laminated is formed by, for example, a vapor phase growth method. In this embodiment, the n-type InP layer 12a and the n-type InP layer 12a and the n-type InP layer 12a and the n-type InP layer 12a and
The thickness of each 3Ga 0.47As layer 12b is approximately 50
[nm], 11 n-type InP layers 12a, n'''
' type io, 53Ga (10 layers of 1,47As layers 12b are formed alternately in sequence to reduce the total thickness of the superlattice structure 12 to 1[
It is set at a little over 3 μm.

Furthermore, the impurity concentration is 1×1015 in contact with the superlattice structure 12.
n-7J below [crn-S] ■nO, 53Ga
A 0.47AS layer 13 is grown to a thickness of about 3 [μm] to form a light absorption region.

See FIG. 2 (1)) As described above, the superlattice structure 12 and the n-type Ino, 53
The semiconductor substrate on which the Ga-0,47A8 light absorption layer 13 has been epitaxially grown is etched into a mesa shape to a depth that reaches the p-type InP substrate 11 as shown in the figure.
fi 0.53-GBo, 47As light absorbing layer 13 surface with anti-reflection coating film 14, mesa etching surface with surface retentive film 1
5 is formed of silicon nitride (S'13N4), etc., and the n(ftll) electrode 16 in contact with the light absorption layer 13 is made of, for example, gold-germanium (AuGe), and p+ type InP is formed using gold-germanium (AuGe). Substrate 11
The p-side electrode 17 in contact with the
).

FIG. 3 shows an energy diagram when reverse pressure is applied to this embodiment having the structure explained above, and in FIG. 3, the same symbols as in FIG. A semiconductor layer is shown. The forbidden band width is approximately 1.35 (eV) for InP and 0.53 Ga for InP.
0.47As is about 0.74 (eV), and I
nP layer 12a and Ifio, 53-Ga0.47As layer 1
Conductor discontinuity △E at the heterojunction interface with 2b
c # 0.2 CeV Single valence band discontinuity △Ev
# 0.4 (eV'3).

The light incident on the APD of this example has an n-type Ifi of 0.53.
-Arise. These electrons flow into the Jill electrode 16, and the holes are injected into the superlattice structure 12, forming the InP layer 12a.
and I n 0.53QB 0.47AS layer 12b.

Holes are transferred from the InP layer 12a to InO, 53Ga0.
When it enters the 47AB layer 12b, it is in a state where it has apparently obtained extra energy by the energy difference ΔEv in the valence band, and the apparent ionization energy decreases and the ionization rate increases. The hole is I n O,53Ga0.47A,8
When entering the InP layer 12a from the layer 12b, the ionization rate decreases, but the electric field applied to the superlattice structure 12
By applying a reverse bias voltage of approximately l0' (V/sub) or higher, the hole energy reaches near the avalanche multiplication threshold and the In0.53Q80.47AS layer 12
When injected into b, avalanche multiplication occurs due to the addition of the above apparent energy.

Electrons generated by avalanche multiplication are also sequentially injected into each layer of the superlattice structure 12 in the direction opposite to that of holes, but because the energy difference ΔEc in the conduction band is small, the effect as in the case of holes is almost non-existent. Therefore, the hole ionization rate β is 10 times or more the electron ionization rate α. As a result of increasing the ionization rate ratio =β/α in this way, the excess noise of the APD of this embodiment becomes sufficiently small.

InP layer 12a and In-0 forming superlattice structure 12
, 53GaO, 47AS layer 12b is approximately 50 (nm) in the above embodiment, but if the thickness of each of these layers is approximately equal to or less than the de Broglie wavelength of the carrier, movement in the thickness direction will occur. A quantum mechanical effect appears and the ionization rate ratio decreases. Therefore, the thickness of each layer is approximately 30 (nm)
It is necessary to make it more than a certain degree.

On the other hand, if the thickness of each layer is made too large, the effect of expanding the ionization rate ratio will be reduced, so it is desirable that the thickness be about 70 (nm) or less.

Furthermore, if the thickness of the avalanche multiplication region is too small, it is necessary to increase the electric field strength in order to give holes the energy necessary for avalanche multiplication.

As the electric field strength increases, the effective ionization rate ratio β of holes and the effective ionization rate ratio α of electrons approach each other. .5×10' [V/ctn] or less, and for this purpose, the thickness of the superlattice structure 1z, which is the droop multiplication region, is at least 0.5 [μm] or more.

Furthermore, in the embodiment, the light absorption region 13 and the layer 12b of the superlattice structure 12 having a narrow band width are formed of n'' type In
Although it is formed by an O,53Ga0.47As layer,
In1-x to lattice match these layers to the InP substrate crystal.
Similar effects can be obtained using a GaXAsyPl-y layer. In this case I n 1-xGaXA syP
The effect of increasing the ionization rate ratio due to the superlattice structure is greater when the composition ratio of l-'l is made as close as possible to the composition ratio of In0.530 & 0.47As (x=0.47, y=l), and β/α is reduced to 10 In order to achieve the above value, it is necessary to set y to about 0.9 or more.

fg+ As described in detail, the present invention has a large one-child efficiency in the wavelength band of 1 [μm] or more, particularly in the wavelength band of 1.3 [μm] to 1.65 (μm). , and I nP
-In It is possible to provide an avalanche photodiode with reduced noise due to the physical property limitations of InGaAs or InGaAsP.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional example of an InP-InGaAs APD, FIGS. 2(a) and (bl) are sectional views showing the main steps of an embodiment of the present invention, and FIG. 3 is a sectional view of a conventional example of an InP-InGaAs APD. It is a figure showing an energy diagram. In the figure, 11 is a p-type InP substrate, 12 is a superlattice structure which is an avalanche multiplication region, and 12a is an n-type InP/if!
, 12 b Id, n-rei') I n O, 5aQa
0.47As layer, 13 is n-type In-〇, 53GB
0.47AS light absorption area, 14 is anti-reflection coating film, 1
5 is a surface protective film, 16 is an n-side electrode, and 17 is a p-side electrode. 11- Sen 1 Town ≠? Prisoner 12- Tada: 5 Figures

Claims (1)

[Claims] An indium-phosphorus compound semiconductor substrate, a semiconductor light absorption region made of an indium-gallium arsenide compound or an indium-gallium-arsenic-phosphorus compound formed by lattice matching to the substrate crystal, and an indium-phosphorus compound semiconductor layer. and an avalanche multiplication region having a superlattice structure in which semiconductor layers made of an indium-gallium-arsenic compound or an indium-gallium-arsenic-phosphorus compound are alternately stacked.