JPH02298082A - Avalanche photodiode - Google Patents

Abstract

PURPOSE:To improve an output response speed of photoelectric current while reducing a noise accompanying with avalanche multiplication by constituting a p-type third semiconductor region formed on a second semiconductor region for avalanche multiplication by three layers while forming a middle layer with lower impurity concentration and greater thickness than the upper and lower layers. CONSTITUTION:A semiconductor layer 6 has a semiconductor layer 7a having high-p-type impurity concentration and relatively thin thickness, a semiconductor layer 7b formed on the semiconductor layer and having low p-type impurity concentration and great thickness compared with the semiconductor layer 7a and a semiconductor layer 7c formed on the semiconductor layer 7b having high p-type impurity concentration and small thickness compared with the semiconductor layer 7b. In this case, the semiconductor layers 7a, 7b and 7c consist, for instance, of InGaAs while having a narrow energy band gap compared with a semiconductor region 4 for avalanche multiplification. Thereby, an optical current comes to be accompanied only by very few noises while a response speed until the photoelectric current is outputted to DC load by being incident of light L can be specially speeded up.

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD 1 The present invention relates to an avalanche F41-diode that can be used to detect light for optical communications. 2. Description of the Related Art Conventionally, an avalanche photodiode has been proposed as described below with reference to FIG. That is, a semiconductor region 1 includes a semiconductor substrate 2 made of, for example, InP and having an n'' type, and a semiconductor layer 3 as a buffer layer formed on the semiconductor substrate 2 and made of, for example, InGaAS and having an n'' type. Further, it is formed on the semiconductor region 1 and contains n-type impurities and p-type impurities.
It has a semiconductor region 4 as an avalanche multiplication layer in which no type impurity is intentionally introduced. In this case, the semiconductor region 4 has a superlattice structure 5 in which two semiconductor layers 5a and 5b made of different materials are stacked alternately, and the semiconductor layers 5a and 5b are made of, for example, in Ga O, 530,47A" and !1 At As. 0,52 0.48 Furthermore, for example, I, which is formed on the semiconductor region 4 and has a narrower energy band gap than the semiconductor region 4,
The semiconductor region 6 includes a semiconductor layer 7 made of nP or InGaAS having a wider energy bandgap than the semiconductor region 4 and having p+ type. Further, an electrode 8 is ohmically attached to the semiconductor region 1 on the side opposite to the semiconductor layer 3 side, and an electrode ohmically attached to the semiconductor region 6 on the side opposite to the semiconductor region 4 side and having a window 10. 9. The above is the configuration of the conventionally proposed avalanche photodiode. According to the avalanche photodiode having such a configuration, the semiconductor layer 7 of the semiconductor region 6 is a semiconductor m Fi
In has a narrower energy bandgap than A4.
P, a reverse bias power source (
Light to be detected having a wavelength corresponding to the energy bandgap of the semiconductor layer 7 of the semiconductor region 6 is applied from outside on the semiconductor region 6, with a DC load previously connected through the semiconductor region 6 (not shown). By making the light enter the inside through the window 10 of the electrode 9, the light is mainly absorbed in the semiconductor region 6, and carriers that are exposed to the light are generated in the semiconductor region 6, and the electrons in the carriers are transferred to the semiconductor region 4. , causing avalanche multiplication in the semiconductor region 4, and outputting the multiplied photocurrent to the DC load.
It can function as an avalanche photodiode. Further, according to the avalanche photodiode shown in FIG. 3, when the semiconductor layer 7 of the semiconductor layer bA6 is made of InAIAS having a wider energy band gap than the semiconductor region 6, the electrode 8 and During the nine
Type II for reverse bias! (not shown) through a DC load (
(not shown) is connected in advance, light to be detected having a wavelength corresponding to the energy band gap of the semiconductor layers 5a and 5b of the superlattice structure 5 of the semiconductor region 4 is transmitted to the outside of the semiconductor region 6. By directing the light to enter through the window 10 of the electrode 9, the light is mainly absorbed in the semiconductor layer ti114, and the light generates carriers (electrons and holes) in the semiconductor region 4, and in the semiconductor M4. The function of an avalanche photodiode can be obtained by a mechanism that generates avalanche multiplication and outputs the multiplied photocurrent based on the avalanche multiplication to a DC load. As described above, according to the conventional avalanche photodiode shown in FIG. 3, the semiconductor region 6 or the semiconductor region 4 acts as a light absorption layer, and the semiconductor region 4 acts as an avalanche multiplication layer. However, the function as an avalanche photodiode can be obtained by
In this case, the semiconductor region 4 as an avalanche multiplication layer
However, it is 0 for mutually different materials jn QaO, 530, 47AS and In At As.
．． 52 0.48 Since each semiconductor WJ 5a and 5b has a superlattice structure 5 in which the semiconductors WJs 5a and 5b are sequentially and alternately stacked, the ratio between the electron ionization rate (α) and the hole ionization rate (β) in the semiconductor region 4 is (α/β) can be obtained with a value sufficiently larger than 1 compared to the case where the semiconductor region 4 has a single layer structure consisting of a semiconductor layer made of Ge or InP instead of having the superlattice structure 5. Therefore, the noise accompanying avalanche multiplication occurring in the semiconductor region 4 is lower than that in the case where the semiconductor region 4 has a single layer structure made of a semiconductor layer made of Ge or InP instead of having the superlattice structure 5. , and therefore, the photocurrent is significantly lower than when the semiconductor region 4 has a single layer structure consisting of a semiconductor layer made of Ge or InP instead of having the superlattice structure 5. It has the characteristic of being accompanied only by noise. [Problem to be solved by the invention 1 However, the conventional avalanche FO shown in FIG. 3]
- In the case of a diode, since the semiconductor layer 7 in the semiconductor layer region 6 has a high n-type impurity concentration, the semiconductor region 6 does not substantially have an accelerating electric field for electrons. The semiconductor layer 7 in the region 6 is the semiconductor layer i,
! In has a narrower energy bandgap than In
When the semiconductor region 6 acts as a light absorption layer by being made of P, the electrons in the carriers generated in the semiconductor region 6 as described above can be absorbed by avalanche multiplication only by diffusion as described above. Semiconductor layer as a layer [4
Therefore, the response speed until the photocurrent is output to the DC load with respect to the incidence of light is relatively slow. In addition, in the case of the conventional avalanche photodiode shown in FIG. 3, since the semiconductor layer of the semiconductor region 6 is made of an AlGa system having a wider energy band gap than the semiconductor region 4, the semiconductor region as an avalanche multiplication layer can be used as an avalanche multiplication layer. 4 also acts as a light-absorbing layer, and the semiconductor region 6 acts as a light-absorbing layer.Even if the above disadvantages can be avoided, the electron ionization rate (α) in the semiconductor layer 4 may be avoided. and hole ionization rate (β),
The ratio (α/β) is more than 1 compared to the case where the semiconductor region 4 has a single layer + M i consisting of a semiconductor layer of Ge or InP'''c@: instead of having a superlattice structure. However, since there are holes in addition to electrons in the semiconductor region 4, the noise accompanying avalanche multiplication is caused by Ge or The present invention has the disadvantage that, although it is less than in the case of having a single layer structure consisting of a semiconductor layer made of InP, there is a relatively large number of defects that cannot be ignored. The purpose of this paper is to propose a new avalanche photodiode that does not have

[Means to solve the problem]

The avalanche photodiode according to the present invention, as in the case of the conventional avalanche photodiode described above in FIG. a second semiconductor region into which neither a type impurity nor an n-type impurity is intentionally introduced;
a third semiconductor region having a mold; (1) first and second electrodes respectively attached to the first and third semiconductor regions, and (2) the second semiconductor regions mutually It has a superlattice structure in which two semiconductor layers made of different materials are stacked alternately in sequence. However, in the avalanche photodiode according to the present invention, in the avalanche photodiode having such a configuration, the third semiconductor region is formed on the first semiconductor layer and the first semiconductor layer, and a second semiconductor layer having a lower impurity concentration and a thicker thickness than the first semiconductor layer; and a second semiconductor layer formed on the second semiconductor layer and having a higher impurity concentration and a thinner thickness than the second semiconductor layer. Further, the first, second and third semiconductor layers have a narrower energy band gap than the second semiconductor region. [Operation/Effect 1] According to the avalanche photodiode according to the present invention having such a configuration, the first and second avalanche photodiodes can be
has a wavelength corresponding to the energy bandgap of the third semiconductor region, particularly the second semiconductor layer of the third semiconductor region, with a DC load connected in advance between the electrodes of the third semiconductor region through a reverse bias power supply. By making the light to be detected enter the inside from the outside on the third semiconductor region, the light is mainly absorbed in the second semiconductor layer of the third semiconductor region, and the third semiconductor! ! Carriers (electrons and holes) based on light are generated in the semiconductor layer of the i region, and the electrons in the carriers reach the second semiconductor region, causing avalanche multiplication in the semiconductor region, and With a mechanism that outputs the rapidly multiplied photocurrent to a DC load, it can function as an avalanche photodiode. “As described above, according to the avalanche photodiode according to the present invention, as in the case of the conventional avalanche photodiode described above in FIG. The second semiconductor region can act as a light absorption layer and the second semiconductor region can function as an avalanche multiplication layer to obtain a function as an avalanche photodiode. Since the second semiconductor region of has a superlattice structure as in the case of the conventional avalanche photodiode described above in FIG.
As in the case of the conventional avalanche photodiode described above in FIG. 3, the ratio (α/β) of the electron ionization rate (α) and the hole ionization rate (β) in the second semiconductor region.
is obtained with a value sufficiently larger than 1 as in the case of the conventional avalanche photodiode described above in FIG. Therefore, as in the case of the conventional avalanche photodiode described above in FIG. 3, the photocurrent is accompanied by significantly less noise. have However, in the case of the avalanche photodiode according to the invention, the first and third semiconductor layers of the third semiconductor region have a high p-type impurity concentration and do not have an accelerating electric field for electrons in them, but the first Since the second semiconductor layer between the first and third semiconductor layers has a low p-type impurity l11 degree, the second semiconductor layer has an applied electric field for electrons, and the first and third semiconductor layers has only a small thickness, so that the second
Electrons in carriers generated in the semiconductor layer 7b reach the semiconductor region 4 more quickly than in the case of the conventional avalanche photodiode described above in FIG. 3 when the third semiconductor region is used as a light absorption layer. do. For this reason, the response speed until a photocurrent is output to a DC load as a guideline for light is as shown in Figure 3 when the third semiconductor region is used as a light absorption layer. It's much faster than that. In addition, in the case of the avalanche photodiode according to the present invention, as described above, the second semiconductor region serving as the avalanche multiplication layer does not act as a light absorption layer, so holes are effectively absorbed into the second semiconductor region. Therefore, as in the case of the conventional avalanche photodiode described above in FIG. It does not have the drawback of relatively large numbers of unavoidable occurrences. [Embodiment 1] Next, an embodiment of an avalanche photodiode according to the present invention will be described with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. The avalanche photodiode according to the present invention shown in FIG. 1 has a similar configuration to the conventional avalanche photodiode described above in FIG. 3, except for the following points. That is, instead of the semiconductor region 6 consisting only of the semiconductor layer 7 made of InP or InGaAs, which has a p+ type, it has a high p-type impurity concentration such as 2 x 1017 cm-'' and a relatively high p-type impurity concentration such as 400A. a semiconductor layer 7a having a small thickness; and a semiconductor layer 7a formed on the semiconductor layer 7a;
A semiconductor II!7b having a p-type impurity concentration lower than that of the semiconductor 117a such as " A semiconductor 17c has a higher p-type impurity S degree than the semiconductor layer 7b such as 500 and a thickness greater than that of the semiconductor layer 7b such as 500.
and has. In this case, the semiconductors IFj7a, 7b, and 7C are made of, for example, InGaAs, and have a narrower energy band gap than the semiconductor region 4. The above is the configuration of an actual example of the avalanche photodiode according to the present invention. According to the avalanche photodiode according to the present invention having such a configuration, a reverse bias power source (not shown) is connected between the electrodes 8 and 9, similar to the case of the conventional avalanche photodiode shown in FIG. The semiconductor region 6 is connected in advance to a DC load (not shown) through the
In particular, the light to be detected having a wavelength corresponding to the energy bandgap of the semiconductor f17b of the semiconductor region 6 is made incident from the outside on the semiconductor region 6 into the inside through the window 10 of the electrode 9. It is mainly absorbed in the semiconductor 117b of the semiconductor layer region 6, and carriers (electrons and holes) based on light are generated in the semiconductor IIJ7b of the semiconductor layer region 6, and the electrons in the chirelia reach the semiconductor region 4, and the The function as an avalanche photodiode can be obtained by a mechanism that causes avalanche multiplication in the semiconductor region 4 and outputs the multiplied photocurrent to a DC load. As mentioned above, according to the avalanche photodiode according to the present invention shown in FIG. 1, as in the case of the conventional avalanche photodiode shown in FIG. The function as an avalanche photodiode can be obtained by making the region 6 act as a light absorption layer and by making the semiconductor region 4 act as a 7 balance multiplication layer. In addition, in this case, the semiconductor region 4 as the avalanche multiplication layer has a superlattice structure 5 as in the case of the conventional 7-balanche photodiode described above in FIG. As in the case of the avalanche photodiode, the ionization rate of electrons in the semiconductor region 4 (
Since the ratio (α/β) of the hole ionization rate (α) to the hole ionization rate (β) is obtained at a value sufficiently larger than 1 as in the case of the conventional avalanche photodiode described above in FIG. As in the case of the conventional avalanche photodiode described above in FIG. 3, the noise accompanying avalanche multiplication occurring in , the photocurrent is accompanied by much less noise,
It has the following characteristics. However, in the case of the avalanche photodiode according to the present invention shown in FIG. 1, as is clear from the electric field intensity distribution shown in FIG.
C has a high p-type impurity concentration and has virtually no accelerating electric field for electrons, but since the semiconductor layer 7b between the semiconductors 17a and 70 has a low p-type impurity concentration, that semiconductor layer 7b has an accelerating electric field for electrons, and since the semiconductor layers 7a and 7C have only a small thickness, the semiconductor layer 7 in the semiconductor T4 region 6 has a
Electrons in the carriers generated in b reach the semiconductor region 4 more quickly than in the case of the conventional avalanche photodiode described above in FIG. 3 in which the semiconductor layer VA6 is used as a light absorption layer. For this reason, the response speed of the lintel, which outputs a photocurrent to a DC load upon incidence of light, is faster than in the case of the conventional avalanche photodiode described above in FIG. It's significantly faster. In addition, in the case of the avalanche photodiode according to the present invention shown in FIG. 1, as described above, the semiconductor region 4 serving as the avalanche multiplication layer is not made to act as a light absorption layer, so that holes are effectively absorbed into the semiconductor region 4. Therefore, as in the case of the conventional avalanche photodiode described above in FIG. 3 when the semiconductor region 4 acts as a light absorption layer, the noise accompanying avalanche multiplication can be ignored. It does not have the disadvantage of relatively high regeneration. Incidentally, in above) E, only one embodiment of the avalanche photodiode according to the present invention is shown, and the structure may be such that the semiconductor layer 3 as a buffer layer is omitted in the semiconductor region 1. The materials of the semiconductor substrate 2 and semiconductor layer 3 of the semiconductor region 1, the semiconductor regions 5a and 5b of the superlattice structure 5 of the semiconductor region 4, and the semiconductor layers 7a to 7C of the semiconductor region 6 are changed from those in the above example. In addition, various modifications and changes may be made to the present invention without departing from the spirit of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of an avalanche photodiode according to the present invention. FIG. 2 is an electric field strength distribution diagram at various positions inside the avalanche photodiode according to the present invention shown in FIG. 1 for explanation. FIG. 3 is a sectional view showing a conventional avalanche photodiode. 1......First semiconductor region 2
...... Semiconductor substrate 3...
...... Semiconductor layer 4 ......
...Second semiconductor region 5a, 5b...Semiconductor layer 6...Third semiconductor region 7.7a, 7b, 7c. ...... Semiconductor layer 8.9...
・・・・・・Electrode 10・・・・・・・・・・・・Window of electrode 9 ・
・・・・・・・・・・・・・・・Earlier applicant Nippon Telegraph and Telephone Corporation Office COC
Hetq made 7t</cm)

Claims (1)

[Scope of Claims] A first semiconductor region having n-type, and a second semiconductor region formed on the first semiconductor region and into which neither n-type impurity nor p-type impurity is intentionally introduced. a third semiconductor region formed on the second semiconductor region and having p-type; and a first semiconductor region attached to the first and third semiconductor regions, respectively.
and a second electrode, and the second semiconductor region has a superlattice structure in which two semiconductor layers made of different materials are alternately stacked one after another. The semiconductor region includes a first semiconductor layer and the first semiconductor layer.
a second semiconductor layer formed on the semiconductor layer and having a lower impurity concentration and a thicker thickness than the first semiconductor layer; and a second semiconductor layer formed on the second semiconductor layer and having a larger thickness than the first semiconductor layer. a third semiconductor layer having a higher impurity concentration and a thinner thickness than the second semiconductor region, and the first, second and third semiconductor layers have a narrower energy band gap than the second semiconductor region. An avalanche photodiode comprising: