JPH03116789A - Superlattice avalanche photodiode - Google Patents

Abstract

PURPOSE:To enable formation of a low noise APD whose ionization rate is lower than that of conventional APD in a wavelength range of 1 to 1.6mum by providing a composition consisting of atom of a specific group, by forming an optical absorbing region of a chemical semiconductor layer which specifies the composition rate and by forming a carrier multiplication layer of a superlattice semiconductor layer which gives a periodic potential. CONSTITUTION:When III-group atom is expressed by AIII, V-group atom is expressed by BV, IV-group atom is expressed by CIV, and a range of x is 0<x<1, a superlattice avalanche photodiode is formed by forming an optical absorbing region of a chemical semiconductor layer whose composition is expressed by (AIIIBV)1-xCIV2x and by forming a carrier multiplication layer of a superlattice semiconductor layer which gives a periodic potential. For example, a Be doped P<+>-GaAs buffer layer 2, a P<->-(GaAs)1-xGe2x (x to 0.3) optical absorbing layer 3, a P<->-AlyGa1-yAs/GaAs superlattice multiplication layer 4, and an Si doped n<+>-GaAs layer 5 are laminated one by one on a Zn doped P<+>-GaAs substrate 1. The superlattice multiplication layer 4 is formed in an inclined potential periodic structure by changing the Al composition gradually from GaAs to Al0.4Ga0.6As.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low-noise avalanche field diode suitable for use as a light receiving element in an optical communication device.

(Prior art and problems to be solved by the invention) As a light receiving element for optical communication in the 1 to 1.6 μm wavelength band with low transmission loss in optical fibers, I no, s) Ga 6
．． 4? iHp/J by heterojunction of A8 and InP
nGaAs heterostructure avalanche photodiode (
(hereinafter abbreviated as APD) has been put into practical use. This AP
D is for injecting holes among the electron and hole carriers generated by absorbing light in InGaAs into InP to cause avalanche multiplication. Here, in InP, the ionization rate β for holes is larger than the ionization rate α for electrons (β/α-2), so
Injecting holes is advantageous in reducing noise. However, in order to achieve even lower noise, it is necessary to develop a material system with a large β/α ratio or α/β ratio.

Therefore, we have proposed a superlattice APD in which different types of semiconductors are alternately stacked to form a periodic potential and electron energy is donated in the conduction band discontinuity ΔE.
Appl, Phys, Lett, 45 by so et al.
．． 1193 (1984) - [Applied Physics Letters Vol. 45, page 1193].

F.

The superlattice APD created by Capasso et al.
It consists of a periodic structure of GaAs and GaAs, and by donating electrons to the conduction band discontinuity ΔE of both materials, ~0.3 eV, the electron ionization rate ratio changes to bulk GaAs.
It is larger than that of As, and as a result α/β-8
I am getting .

However, the AjlGaAs/GaAs superlattice has the disadvantage that it cannot receive light in the wavelength range of 1 to 1.6 μm, which is optimal for optical communication. Instead, the InAJAs/InGaAs superlattice structure lattice-matched to InP has photosensitivity in the above wavelength range;
There is no report that the electron ionization rate α is improved in the nAJ As/InGaAs superlattice structure.The reason for this is I, which is the narrow energy gap where avalanche multiplication occurs.
This is because nGaAs is a ternary mixed crystal, so mixed crystal scattering of carriers (scattering based on potential fluctuations) hinders the ionization phenomenon. Furthermore, another reason is that InAjAs, which has a wide energy gap, is also a mixed crystal, and the energy difference between the valleys (gamma valley and L valley) in the conduction band is small, so it is susceptible to carrier scattering, and therefore the average energy of electrons is This is because the improvement is not sufficient to promote ionization.

Therefore, the purpose of the present invention is to eliminate the above-mentioned drawbacks and to
, 6 μm wavelength range, the objective is to provide a low-noise APD with a higher ionization rate ratio (α/β) than conventional APDs.

(Means for Solving Task U) The present invention is based on the following method: When group (I) atoms are represented by AI, group V atoms are represented by By, and group (II) atoms are represented by Cm, and the range of X is O<x<1, the composition is ( This is a superlattice APD characterized in that a layer of a compound semiconductor represented by AlBy) + - Cff2 is used as a light absorption region, and a superlattice semiconductor layer giving a periodic potential is used as a carrier multiplication layer. This superlattice APD of the present invention
Then, the above (Am Bv) 1-Cyt- is (GaA
s)+−+cGetx, and the superlattice semiconductor layer is Aj−
It is preferable to have a periodic structure of yGal-yAs/GaAs.

(Action/Principle) (A m B v ), -14Cyl engineering (G a
A s ) t -zG e x *, and the superlattice semiconductor layer is A y G a 1-y A s / G a
The operation and principle of the present invention will be explained using a structure consisting of an As periodic structure as an example.

In the present invention, the GaAs material used in the short wavelength region of 0.7 to 0.8 μm is intentionally applied to the long wavelength region of 1 to 1.6 μm. A GaAs) l-x G ett mixed crystal semiconductor is used as the light absorption region.

(GaAs) I-*Ge=x mixed crystal is K, E, Ne
Journal of Wman and J.D. Dow
Vacuum Science and Technology - Volume 81, No. 2
As reported in No. 243-245, the forbidden band width shows composition X dependence as shown in Fig. 4, that is,
Strong ionic bond Ga As and covalent Ge
By mixing the energy curvature (Bowi
ng) is large, so the cutoff wavelength λ' is large in the wide range of X of 0.2≦X≦0.9. is 1.24
/E, λ. It is 21.5 μm, and has sufficient photosensitivity in the long wavelength range. (G a As
) Of the electron-hole pairs generated by photoexcitation in I-xGexx, the electrons are lattice-matched to AJyGa+-AAs.
/GaAs is injected into the superperiodic layer to improve the ionization rate α for electrons. Figure 3 shows this situation. In FIG. 3, (G a As ) I-zG
exx"C' The generated electrons are A j y G a r
-yA S /GaAs periodic layer is implanted. AJ for electronics.

Since energy is provided by the conduction band discontinuity ΔEc between Ga + -y As and GaAs, ionization becomes easy. As a result, the α/β ratio increases.

(Example) FIG. 1 shows a pharyngeal view of an APD that is a first example of the present invention. In FIG. 1, Zn-doped P''-
On the GaAs substrate 1, molecular beam epitaxial (MBB)
) Be-doped P-GaAs buffer layer 2,
P--(GaAs) rt Ge2t(x~O-3
>Light absorption layer 3, P--A, Q y Ga+-y As
/GaAs superlattice t1 layer 4, Si-doped n”G
Two aAs layers 5 were sequentially laminated. The growth temperature was 600°C. The light absorption layer 3 has a thickness of 1 to 2 in order to obtain sufficient quantum efficiency.
It is laminated to a thickness of ALm (f). Superlattice multiplication layer 4
As shown in Fig. 3, from GaAs to Ajo, < G
The Aj composition was gradually changed up to ao, a A S to form a gradient potential periodic structure. The period 0 was approximately 500 people and the number of periods was 10. Using normal exposure technology, etching was performed in a mesa shape, and the mesa side walls were etched. 6 is an n-side electrode made of an AuGe alloy, and 7 is a PpI electrode made of an AuZn alloy, the surfaces of which are protected by a SiNx surface protection film 8 formed by plasma CVD, and each is formed by a normal resistance heating vapor deposition method.

FIG. 2 is a sectional view of an APD which is a second embodiment of the present invention. In FIG. 2, the lamination method is the same as the first embodiment described above (MBE method, but the substrate is n"-GaAs and P
"-(GaAs)r-*Ge 21E is used as a light absorption region. The method for manufacturing the diode is the same as in the first embodiment.

Both APDs in FIGS. 1 and 2 apply a reverse bias electrode between the P(IIJ electrode and the n-side electrode, and extend the depletion layer from the n+P junction or the P''n junction toward the substrate side.
The figure is an energy band diagram of the APD shown in FIG. 2 when a reverse bias voltage is applied.

P'' (GaAs) r-t Electrons generated in the Ge2z layer 3 are injected into the AjGaAs/GaAs periodic layer 4,
Energy is obtained by ΔE6, leading to ionization.

(Effects of the Invention) The APDs fabricated in the first and second examples described above exhibited a high quantum efficiency of 70 to 80% at a wavelength of 1.55 μm. Furthermore, the ionization rate ratio α/β is in the range of 5 to 2o, which is compared to InP/InG, which is a conventional long wavelength band APD.
There was a significant improvement in the β/α ratio of aAs heterozygous APD compared to 2.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing the cross-sectional structures of APDs according to first and second embodiments of the present invention, respectively. Figure 3 is an energy band diagram during operation, Figure 4 is (GaAs)
FIG. 3 is a characteristic diagram showing the forbidden band width with respect to the composition of l-K Getx. In the figure, 1 is the substrate, 2 is the buffer r layer, and 3 is (Ga
A S ) I - & G e *z light absorption layer, 4 is Aj. A Ga+-y As/GaAs hyperperiodic layer, 5 is a GaAs layer, 6 is an n1ll electrode, 7 is a P-side electrode, and 8 is a surface protective film.

Claims (1)

[Claims] When a group III atom is represented by A_III, a group V atom is represented by B_V, and a group IV atom is represented by C_IV, and the range of x is 0<x<1, the composition is (A_IIIB_V)_1_-_xC_I
A superlattice avalanche photodiode characterized in that a compound semiconductor layer represented by V_2_x is used as a light absorption region, and a superlattice semiconductor layer giving a periodic potential is used as a carrier multiplication layer.