JP2656476B2 - Semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor device having a quantum well structure formed by a heterojunction of a compound semiconductor. In particular, the present invention relates to a structure in which donors and acceptors are spatially non-uniformly doped in the well layer of the structure.

[Conventional technology]

The compound semiconductor quantum well structure has been applied to the active layer of a multiple quantum well semiconductor laser, an optical switch using high-speed modulation of the complex refractive index by an electric field, etc. ("Physics and Applications of Semiconductor Superlattices" Society edition, Baifukan Showa 59
Year). As shown in FIG. 3 (a), the structures used for these structures consist of heterojunctions of compound semiconductors having different band gaps, and have a conduction band discontinuity ΔEc and a valence band discontinuity ΔEv. Each forms a potential barrier for electrons in the conduction band and holes in the valence band. FIG. 3 (b) shows a so-called doping superlattice in which the same semiconductor is periodically doped with a donor and an acceptor. As schematically shown in FIG. 3, electrons and holes are spatially separated. In this system, when the number of electrons in the conduction band and the number of holes in the valence band change due to light absorption, the shape of the potential barrier changes to self-consistent in order to satisfy the electrical neutral condition. Therefore, since the quantum level changes sequentially according to the intensity of the incident excitation light, LLChang et al., "Synthetic Modulated Structure", Academic Press, 1985, p. 241 (“Sy
nthetic Modulated Stracture ", Academic Press, (198
5) As shown in p.241), the light absorption coefficient emission spectrum can be tuned by external light. FIG. 3C shows an example in which pocket quantum wells for electrons and holes are added to FIG.

In the example of FIG. 3A, when an external electric field is applied to the entire quantum well, the electron wave function and the hole wave function shift in opposite directions as shown on the right side of FIG. Although the complex refractive index response to light changes, the quantum level of electron holes confined in the well does not change much compared to the example of FIG. 3 (b), so that it can be said to be a wavelength tuning characteristic. No change.

[Means for solving the problem]

An object of the present invention is to combine the characteristics of the conventional composition type quantum well and doping type quantum well, i.e., a semiconductor crystal which is spatially non-uniformly doped, has a larger band gap than this crystal, and Band discontinuities in the conduction and valence bands are achieved by introducing a new quantum well structure sandwiched by a second semiconductor that forms a barrier in the crystal.

[Action]

FIG. 1 (a) is a conceptual diagram illustrating the basic operation of the present invention.
It was shown to. In the example shown here, the well layer is composed of one p / n junction, and is sandwiched on both sides by undoped hetero barrier layers having large ΔEc and ΔEv. Electrons in the conduction band are confined in the n-type doped region of the well layer and holes in the valence band are confined in the p-type doped region of the well layer by creating quantum levels. The electric neutral condition in the well is satisfied by the balance of ionized donor, acceptor, free electron and hole shown in the figure, and the potential of the well layer is obtained by solving Poisson equation and Schlesinger equation in a self-consistent manner. Can be FIG. 1B shows an approximate potential distribution in the case of a multiple quantum well. Here, the electrons that have risen from the ground level of holes to the conduction band due to the incidence of light of energy E ₁ are relaxed to the ground level of electrons, but the luminescence transition from this level to the valence band (energy E ₂ > E ₁ ) The transition is not possible because the valence band is full, and as a result, a large amount of electrons and holes are accumulated in the well layer in a spatially separated state.
As a result, the potential in the well layer changes self-consistently so as to satisfy the electrical conditions again, and the quantum levels of electrons and holes also change greatly.

As described above, in the quantum well of the present invention, as a result of incorporating the features of the two types of quantum wells shown in FIG. 3, a nonlinear optical-optical interaction function with an increased design freedom is realized. become able to.

〔Example〕

Hereinafter, the contents of the present invention will be described based on examples. As an example of the quantum well structure shown in FIG. 1 (a), p of In _0.53 Ga _0.47 As lattice-matched to InP is added to the well layer using InP as a barrier layer.
In the example using the / n junction, crystal growth was performed by a reduced-pressure MOCVD apparatus capable of producing a quaternary system of InGaAsP. Further, In _0.52 Al _0.48 As lattice-matched to InP is used as a barrier layer, and In _0.53 Al
An example using a Ga _0.47 As p / n junction was produced by an MBE apparatus.
In both cases, the aim was to fabricate a light-to-light modulation detector as shown in FIG.
The nP (or InAlAs) cladding 2 is 1 μm, and the quantum well structure of the present invention 3: InP / (p / n) InGaAs / InP or InAlAs / (p / n) I
1 μm nGaAs / InAlAs, undoped InP (or InAlAs)
After growing the cladding 4 of 1 μm, a part of InP of the substrate was removed. In the arrangement in which incident light (wavelength λ ₁ ) and monitor detection light (wavelength λ _C ) are incident on the quantum well layer in the vertical direction or the parallel direction, while changing the incident light intensity of λ ₁ ,
The transmission intensity and phase shift of _C light were observed. A Michelson-type interference detection method was used for phase detection. As the wavelength lambda ₁ (schematic view references under the second diagram (a)), the hole ground level in the well in the p-type region shown in FIG. 1 (b) to the excitation energy E ₁ to the conduction band A wavelength equal to the detection light wavelength λ ₂ was selected to be equal to the transition energy E _C from the electronic ground level to the valence band in the n-type region in the well in FIG. 1B. As the incident light intensity increases, electrons and holes are spatially separated and accumulated in the well. As a result, the quantum level shifts, and the complex refractive index of the quantum well viewed at the wavelength λ ₂ changes continuously. As a result, it was found that the presence or absence of the incident light could be detected with the same high sensitivity by the attenuation factor of the transmitted light and the phase shift. The response speed when a pulse laser was used as the incident light was equal to or higher than the speed of a conventional optical switch in which an electric field was applied to a GaAs / GaAlAs-based quantum well. This is because, in the quantum well of the present invention, electrons excited in the conduction band at lambda ₁ light, and scattering of high concentrations of ionized impurities, shows that relaxed to rapidly ground level by the internal electric field gradient I have.

In addition, as shown in FIG. 2 (b), similarly to the example of the conventional doping superlattice, the pn layer in the quantum well is independently pn layer.
It was confirmed that a photodetection layer could be formed by using a type ohmic electrode.

In the above, an example of a quantum well using InP, InGaAs, and InAlAs on an InP substrate has been shown, but it is clear that the content of the present invention does not impose any limitation on the material.

Further, not only a single p / n junction but also a p, n, i layer or the like may be added to a part of the well as needed, so that a more subtle quantum level modulation effect can be expected. In some cases,
By creating a very low hetero-barrier layer in the well, the spatial separation of electron holes can be made more effective.

〔The invention's effect〕

According to the present invention, since a hole and an electron are separated and confined in the quantum well layer, a new functional optical device having strong nonlinearity can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a quantum well structure of the present invention, FIG. 2 is a diagram showing an InP / (p / n) InGaAs / InP structure as an embodiment of the present invention, and FIG. It is a figure which shows two types of quantum well structures.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takao Miyazaki 1-280 Higashi-Koigabo, Kokubunji-shi, Hitachi, Ltd. Central Research Laboratory Co., Ltd. (56) References JP-A-62-285227 (JP, A)

Claims (3)

(57) [Claims] A first semiconductor layer including at least one quantum well structure formed by sandwiching the first semiconductor layer with a second semiconductor layer having a larger forbidden band width than the first semiconductor layer; A semiconductor device, wherein the first semiconductor layer includes a first region layer of a first conductivity type and a second region layer of a second conductivity type. 2. The semiconductor device according to claim 1, wherein said first region layer and said second region layer form a pn junction. 3. The method according to claim 1, wherein the first semiconductor layer is Ga _0.47 In _0.53 As, and the second semiconductor layer is InP or Al _0.48 lattice-matched to InP.
2. The semiconductor device according to claim 1, wherein In _0.52 As is set.