JPS63207186A - Material for visible-light region optical element - Google Patents

Abstract

PURPOSE:To increase transition probability by shifting an indirect transition type semiconductor to a direct transition type semiconductor by introducing superlattice structure to the indirect transition type semiconductor or applying pressure to it. CONSTITUTION:An indirect transition type semiconductor is formed in superlattice structure. Or pressure is applied to the superlattice structure of the indirect transition type semiconductor. Consequently, the indirect transition type semiconductor is shifted to a direct transition type semiconductor. As a result, the band gap of a visible light region larger than a normal III-V direct transition type semiconductor is shaped while interaction with beams can be increased. Accordingly, an optical element having high efficiency is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a semiconductor material for optical devices that is highly efficient in the visible light region.

[Conventional technology]

Until now, light-emitting devices in the visible light region have utilized an isoelectronic trap formed by adding nitrogen to GaP, which is an indirect transition type semiconductor, and optical transition via this trap. However, in this process, the transition probability does not become large enough to cause laser oscillation.

Furthermore, in the past, an application has been filed for a semiconductor device using a superlattice made of the same kind of material as the present invention (Japanese Patent Laid-Open No. 59-197187). The superlattice structure claimed there is based on the following conditions: 2≦m≦7 2≦n≦7 n+m≦12, where m is the number of GaP molecular layers included in one superlattice period and n is the number of AβP molecular layers. The goal is to satisfy the following.

[Problem that the invention seeks to solve]

However, the significance of this condition is not physically clear, and as a result of actual calculations, some semiconductors are not direct transition type semiconductors, and even if they are direct transition type semiconductors, the interaction with light is weak and the quantum efficiency is low. It was found that the material contained a structure that would not make it a good material. In particular, the luminous efficiency in the case of n=m=4, which is cited as an example, is expected to be extremely low (about 3 orders of magnitude lower than that of a direct transition type semiconductor) as described later (see FIG. 2). Therefore, such condition settings cannot be used as a reference in producing materials or devices.

The present invention has been made in view of these points, and its purpose is to have a band gap in the visible light region that is larger than that of ordinary I/V group direct transition type semiconductors, and which has a high interaction with light. The object of the present invention is to provide a semiconductor material for realizing an optical device with a large amount of energy and therefore high efficiency.

[Means for solving problems]

In order to achieve such an object, the present invention converts an indirect transition type semiconductor into a direct transition type semiconductor by making the indirect transition type semiconductor into a superlattice structure or by applying pressure to the superlattice structure of the indirect transition type semiconductor. It was designed so that it would be transferred to.

[Effect]

In the material for optical devices in the visible light region according to the present invention, the transition probability is enhanced.

〔Example〕

In order for indirect transition type semiconductors to cause optical transition, momentum supply through phonon scattering and the like is essential. For this reason,
An indirect transition process is represented by a quadratic process, and its transition probability usually exhibits a small value. Generally, among II[/V group semiconductors, a material having a band gap corresponding to the energy of light in the visible light region is an indirect transition type semiconductor. Therefore, until now, light-emitting devices in the visible light region have utilized an isoelectronic trap formed by adding nitrogen to GaP, which is an indirect transition type semiconductor, and optical transition via this trap. However, in this process, the transition probability does not become large enough to cause laser oscillation.

The present invention provides a material for an optical device in the visible light region, in which an indirect transition type semiconductor is transferred to a direct transition type semiconductor by introducing a superlattice structure into the indirect transition type semiconductor or applying pressure. This increases the transition probability.

First, a case will be described in which a superlattice structure is introduced into an indirect transition type semiconductor. The superlattice structure is formed by growing GaP and ARP, both indirect transition type semiconductors, in the (001) direction.

That is, the formation of a GaP/Aj2P (001) superlattice. Here, both of these materials have conduction band bottoms at the X point, and the bandgaps are 2635 and 2.5, respectively.
It is 0eV. Furthermore, these materials have very similar lattice constants, making it possible to create a superlattice with almost lattice matching.

The transfer between indirect transition and direct transition based on the introduction of a structure such as a superlattice is caused by the band folding effect and the band mixing effect. It has been completely ignored, and has been carried out based on a physically meaningless image. The present invention was proposed after confirming the band structure in all Prillouin zones based on actual theoretical calculations.

The preconditions for superlattice analysis are shown below.

■ To improve the accuracy of conduction band reproduction, normal SP”
A 5p3s'' strong coupling method was used in which an excited S state S'' was added to the basis. This can be seen, for example, in ``Vogl, Hjalmarsson and Dow, Journal of Physical Chemistry, Solid State Science, Vol. 44, p. 365, 1983J (P. Vogl, 11.tljarm
arson & J, D, Dow, J, Phys, Che.
m, 5olids, 44. p, 365.1983)
It is described in.

■ In order to improve the accuracy of conventional analysis, even second-proximity interactions were taken into account.

In other words, the analysis of the superlattice consists of each molecular layer (cation-anion-pair).
Based on the two-dimensional wave function corresponding to 1ψ〉=Σr((2)1φ(m)〉+Σf (n) l
φ(n)〉・・・(1) Purification W of the specification (no change in content H = vomit q mouth 2 zoku - shikugure k (machi (+1 () Using the wave function that becomes (2) Hamiltonian (H
amiltonian) This corresponds to diagonalizing H. The matrix elements of Hamiltonian are (3)
- Contains a 5×5 submatrix shown in equation (7).

Equation (5) represents the second neighbor interaction within the molecular layer, and (6)
Equation (7) represents the first proximity interaction, and equation (8) represents the second proximity interaction between molecular layers.

As an analysis result, FIG. 1 shows the transition between indirect transition and direct transition due to the structural change of this superlattice. In Figure 1, m+n≦10 (m: number of GaP molecular layers, n: Aj2
Structures that are direct transition type semiconductors among all combinations within the range of P molecular layer number are indicated by ○. Therefore,
Only the superlattice with the structure indicated by the circle in FIG. 1 is effective as a material for optical devices (particularly light emitting devices). However, being a direct-transition semiconductor is only a necessary condition for the material to be effective; in addition, the magnitude of the material's interaction with light must be evaluated.

FIG. 2 shows the superlattice structure dependence of the oscillator strength f, which is a parameter representing the magnitude of the interaction between matter and light.

In FIG. 2, the horizontal axis shows the period mn (atomic layers) of the superlattice, the vertical axis shows the oscillator strength f, and the dotted line S shows the oscillator strength f of rlsV to rlc of bulk GaP. In addition, ○,・ indicate the case where m+n=odd number, △,mu indicate the case where m+n-even number, ○, △ indicate the case where m+n=N, m, n
The value of the combination that gives the maximum oscillator strength f among all combinations of is shown. Similarly, .mu. and .mu.indicate the value of the combination that gives the minimum oscillator strength f. From FIG. 2, it can be seen that the more odd numbers m and n are, and the smaller m+n, the greater the vibrator strength f, and therefore the greater the interaction with light, making it more effective as a material for optical devices.

Next, the structure dependence of the band gap of these superlattices is shown in FIG. In FIG. 3, the horizontal axis indicates the number n of AβP atomic layers included in one superlattice period, and the vertical axis indicates the band gap. Also, if ○ is m + n = 4,
Symbol indicates the case where m+n=s, × indicates the case where m+n=1Q, Δ indicates the case where m+n=20, and O indicates the case where m+n=30.

From Figure 3, the bandgap of the GaP/AIP superlattice is the bandgap of GaP, 2.35eV, and Aj
It can be seen that the band gear knob of 2P is between 2.50 and approximately belongs to the green area. Finally, from the above,
(m, n) is (LL), (1, 3L (L5L(3, 3)
, (5,1), (L7), (3,5), (5,3L(7
, 1) with the structure G a P / A j2 P (
001) Superlattices are effective as materials for optical devices in the visible light region.

Next, a case will be described in which pressure is applied to the superlattice structure of an indirect transition type semiconductor to transform it into a direct transition type semiconductor. When pressure is applied to a semiconductor, the band structure changes, but the way the band structure changes depends on the position of the Prillouin zone. In particular, when the hand structure itself has anisotropy, such as a superlattice, the hand structure can be artificially changed to some extent depending on the direction of the applied pressure.

Figures 4 to 6 show that the GaP/AffiP (001) superlattice has l
Indirect transition when a pressure of Q k b a r is applied /
The transition between direct transitions is shown. In Figures 4 to 6, ○ indicates a direct transition type structure, and ◎ indicates the structure in Figures 1 and 4.
As is clear from the comparison of FIGS. 6 to 6, the structure shows a transition from an indirect transition type to a direct transition type upon application of pressure. ◎ is included in -1 lattice period (number of GaP molecular layers,
A/! As a combination of P molecular layer number), m and n are odd numbers,
and m+n<12, and the structure is shown when pressure is applied in a direction parallel to the superlattice plane or hydrostatically.

From Figures 4 to 6, when pressure is applied in the direction of the superlattice axis, most cases become indirect transition type, and when pressure is applied hydrostatically or in the superlattice in-plane direction, it becomes direct transition type. You can see that there will be a lot of things.

Thus, in the Ga P/AA P(001) superlattice, the effective structural freedom can be increased by applying pressure hydrostatically or in the superlattice in-plane direction.

In the above example, we proposed a superlattice structure that is effective as a material for optical devices based on analysis limited to the G a P / A 7IP superlattice. Basically, similar behavior can be seen in the superlattice. For example, G a P / Z n5Se, A
EP/ZnSSe, , Si/GaP, A1 A s /
A superlattice formed by a combination of semiconductor materials such as ZnSe is useful as a material for optical devices.

〔Effect of the invention〕

As explained above, the present invention transforms an indirect transition type semiconductor into a direct transition type semiconductor by making the indirect transition type semiconductor into a superlattice structure or by applying pressure to the superlattice structure of the indirect transition type semiconductor. By this, the normal I[[
It has a larger bandgap in the visible light region than the /V group direct transition type semiconductor and can increase interaction with light, so it has the effect of realizing a highly efficient optical device.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the transition between indirect transition and direct transition due to structural changes in the GaP/Aj2P(001) superlattice, and Figure 2 is an illustration of the oscillator strength at point r of the GaP/AIP superlattice. Graph showing structural dependence, Figure 3 is GaP
/A/! Graphs showing the structure dependence of the direct gap size of P(001) superlattice, Figures 4 to 6 are for Ga P
/A6 P(001) An explanatory diagram showing the analysis results of the transition between indirect transition/direct transition when a pressure of 10 kbar is applied to the superlattice in the superlattice axis direction, hydrostatically, or in the superlattice in-plane direction. be.

Claims (3)

[Claims] (1) The indirect transition semiconductor is transformed into a direct transition semiconductor by forming the indirect transition semiconductor into a superlattice structure or by applying pressure to the superlattice structure of the indirect transition semiconductor. Materials for optical devices in the visible light region. (2) The superlattice is a GaP/AlP (001) superlattice, and the number m of GaP molecular layers included in one superlattice period and the Al
The combination (m, n) with the number n of P molecular layers is (1, 1) (1,
3), (1, 5), (3, 3), (5, 1), (1, 7
), (3,5), (5,3), (7,1), the material for a visible light region optical device according to claim 1. (3) The superlattice is a GaP/AlP (001) superlattice, and the number m of GaP molecular layers included in one superlattice period is
As a combination with the number n of P molecular layers, m and n are odd numbers,
The material for a visible light region optical device according to claim 1, characterized in that m+n≦12.