JP2578924B2 - Compound semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is not suitable for growing relatively thick epitaxial crystals such as metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE). The present invention relates to a semiconductor light emitting device having high uniformity and high output light emitting characteristics, which is manufactured by using an epitaxial crystal growth method having sufficient controllability and uniformity even for an extremely thin film of the order.

[Conventional technology]

Conventionally, there are vapor-phase epitaxy (VPE) and liquid-phase epitaxy (LPE) as epitaxial crystal growth methods for thick films, both of which have a growth rate of 10 μm / hr or more, and are indispensable for producing semiconductor light emitting devices. Technology.

However, the VPE method is not suitable for growing a compound semiconductor containing Al, and for example, a structure having an Al _X Ga _{1 -X} As heterojunction cannot be produced.

In addition, the LPE method can grow a compound semiconductor containing Al, and can create a structure such as an Al _X Ga _1-X As / GaAs heterojunction. Although the device has a high light output, uniformity and reproducibility are poor, and it has been difficult to obtain a semiconductor light emitting device with high yield.

In contrast, MOVPE and MBE methods are not suitable for thick-film crystal growth, but can produce ultra-thin films of the order of 1 nm with good controllability, and can easily form heterojunctions containing Al. It has excellent uniformity and reproducibility.

[Problems to be Solved by the Invention] However, the conventional compound semiconductor light emitting device having a heterojunction prepared by the MOVPE method or the MBE method does not have a high light output because it is not a thick film, and has characteristics of high uniformity and high reproducibility. I couldn't make the most of it.

The present invention is intended to solve the above-mentioned problems, and the MOVPE
It is an object of the present invention to improve a light output while maintaining or improving uniformity and high reproducibility in a compound semiconductor light emitting device having a heterojunction formed by a method and an MBE method.

[Means for solving the problem]

Generally, in the multilayer structure shown in FIG. ₃ , when light having a wavelength λ ₀ is incident on a layer having a refractive index of n ₂ and a layer (substrate) having a refractive index of n ₃ perpendicularly from a layer having a refractive index of n ₁ , the reflectance R _⊥ becomes It is expressed as the following equation.

here, When R _{に な}る becomes maximum, it depends on the magnitude relation of n ₁ , n ₂ , n ₃ , and the following case is considered.

n ₂ <n ₁ <n ₃ this time _{r 1> 0, r 2 <} 0 ∴r 1 r 2 <0 Thus, the R _⊥ is maximized, there when that maximizes the denominator of (1) , Which is when cos 2δ = −1 is satisfied. At this time, Therefore, Incidentally, from _{n 2 <n 1 <n 3} , n 2 2 < thus _{n 1 n 2 <n 2 n} 3 n 1 n 2 <n 1 2 <n 1 n 3, is n ₁ n ₃ <n _{² 2} . Thus, the refractive index that satisfies the expression (2)
By providing a layer of n _2, since this layer acts as a reflective layer such that the maximum reflectance, that some or most of the light which has been absorbed in the conventional back surface taken from the surface side is reflected Therefore, a high light output can be obtained.

The configuration of the reflective layer does not need to be a single layer, and may have a multilayer structure. In this case, the average refractive index of the reflective layer should correspond to n ₂ in FIG. 3, and the total film thickness should correspond to d, and a multilayer structure can be designed in which the average refractive index increases R _⊥ .

The derivation of the reflectance in the case of a multilayer structure will be briefly described below.

For example, consider a multilayer film composed of N layers as shown in FIG. 4, where each film thickness is D _k (k = 1, 2,..., N) and the refractive index is n _k (k
= 1,2,3, ..., N), and light of wavelength λ ₀ is vertically incident (φ = 90
゜), the following optical matrix _Ak corresponds to each layer.

However, w _k = n _k cos φ = n _k i ² = −1 The optical matrix A corresponding to all layers is In other words, assuming that w ₀ = n ₀ and w _g = _ng , the reflectance ＲR ^(M) _⊥
▼ is It is expressed as

[Action]

The present invention provides a reflection layer having a different refractive index from the Al _X Ga _1-X As between the GaAs substrate and the Al _X Ga _1-X As layer on the substrate side, and the GaAs substrate, When the refractive indexes of the layer and the Al _X Ga _1-X As layer are respectively n ₃ , n ₂ and n ₁ , these refractive indices are
By satisfying n ₂ <n ₁ <n ₃ , part or most of the light absorbed on the back surface is reflected and extracted from the front surface side, so that a high light output can be obtained. By doing so, it is possible to specifically increase the reflectance with respect to incident light of a predetermined wavelength, and to improve the crystallinity of the upper layer to improve the luminous efficiency.

〔Example〕

 Hereinafter, examples will be described.

Embodiment 1 FIG. 1 is a view showing one embodiment of a hetero-junction high-brightness light emitting LED according to the present invention, wherein 1 is a lower ohmic electrode and 2 is GaAs: Z.
n substrate, 3 a reflection layer, 4 a P cladding layer (P-Al _X2 Ga
_1-X2 As), 5 is a p-active layer (p-Al _Y Ga _1-Y As),
Reference numeral 6 denotes an n-cladding layer (n-Al _X1 Ga _1-X1 As), and reference numeral 7 denotes an upper ohmic electrode.

In the figure, as the structure of the epitaxial layer, the n cladding layer 6 has x ₁ = 0.7 and a carrier concentration n = 1 × 10 ¹⁸ c
m ⁻³ , thickness d ₁ = 5 μm, p-active layer 5 has y = 0.3
5. Carrier concentration p = 1 × 10 ¹⁷ cm ⁻³ , thickness d ₂ = 1.5 μm,
The P cladding layer 4 has x ₂ = 0.7, carrier concentration p = 1 × 10
¹⁸ cm ^-3 and thickness d ₃ = 5 μm.

As the reflection layer 3, AlAs (carrier concentration p = 1 × 10 ¹⁸ cm)
^-3 ) The thickness d ₄ = 111 nm is used. The refractive index n ₁ of the P cladding layer 4 at the emission wavelength of the p active layer n ₁ = 3.25;
The refractive index of the reflective layer 3 is n ₂ = 2.97, and the refractive index of the substrate 2 is n ₃ = 3.77. Therefore from equation (3), R _⊥ is When not using a reflective layer, Thus, the reflectivity was improved about five times.

(Example 2) Next, an example in which the reflection layer is formed of a multilayer thin film as schematically shown in Fig. 2 will be described.

The structure of the reflective layer is determined by the emission wavelength of the p-active layer (λ ₀ =
In _{660nm), n 1 · D 1} = λ 0/4 = 165nm n 2 · D 2 = λ 0/4 = 165nm n 0 = 3.25 y = 0.9 n 1 = 3.05, D 1 = 5.55nm z = 0.4 n 2 = 3.45, when D ₂ = 47.8 nm, w ₁ = n ₁ w ₂ = n ₁ ∴δ ₁ = δ ₂ = π / 2 Therefore, when Al _Y Ga _1-Y As / Al _Z Ga _1-Z As is composed of one layer, Becomes

Therefore, the reflectance R _⊥ ^(M) (l) is n _g = 3.77 (GaAs)
As When 1 is finite, for example, when l = 15, _R⊥ ^(M) (15) = 0.89, and the reflectance can be made closer to 1.

〔The invention's effect〕

As described above, according to the present invention, part or most of the light absorbed on the back surface is reflected and radiated to the front surface, so that the light output can be increased. By doing so, the crystallinity of the upper layer is increased and the internal luminous efficiency is also increased, so that the two effects are synergistically obtained, and a semiconductor light emitting device with high light output can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the structure of a compound semiconductor light emitting device according to the present invention when the reflection layer is constituted by a single-layer thin film, and FIG. FIGS. 3 and 4 are diagrams showing the structure of the compound semiconductor light emitting device in the case where the reflection layer is provided, and are diagrams for explaining the reflectance when the reflection layer is a single layer and a multilayer. 1 ... lower ohmic electrode 2 ... GaAs: Zn substrate 3 ...
Reflective layer, 4 ... P clad layer (P-Al _X2 Ga _1-X2 As), 5
... P-active layer (p-Al _Y Ga _1-Y As), 6 n-cladding layer (n-Al _X1 Ga _1-X1 As), 7 upper ohmic electrode.

Claims (3)

(57) [Claims] In a double heterojunction semiconductor light emitting device using Al _X Ga _{1 -X} As as a carrier confinement layer and a light extraction layer, a GaAs substrate and Al _X Ga _{1 -X} As on the substrate side are provided.
A reflective layer having a refractive index different from that of the Al _X Ga _1-X As, and the refractive indexes of the GaAs substrate, the reflective layer, and the Al _X Ga _1-X As layer are each set to n ₃ when the n ₂ and n _1, a compound semiconductor light emitting device characterized by these refractive indices satisfy the relationship _{n 2 <n 1 <n 3} . 2. The compound semiconductor light emitting device according to claim 1, wherein said reflection layer is a single layer. 3. The reflection layer according to claim 1, wherein two or more Al _X Ga _{1 -X} As layers having mutually different refractive indices are alternately laminated.
20. The compound semiconductor light emitting device according to claim 20