JP2699661B2 - Semiconductor multilayer reflective film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor multilayer reflective film having a low resistance.

[0002]

2. Description of the Related Art As a light emitting device suitable for parallel optical information processing and parallel optical communication, there is a vertical cavity surface emitting laser which can be parallelly arranged in a plane. FIG. 5 is a sectional view of a general vertical cavity surface emitting laser. An n-type semiconductor multilayer reflective film 13 is formed on the n-type GaAs substrate 1 in order. An n-type Al _0.3 Ga _0.7 As clad layer 4 and an i-In _0.2
A Ga _0.8 As active layer 5, a p-type Al _0.3 Ga _0.7 As clad layer 6, and a p-type semiconductor multilayer reflective film 14 are sequentially grown.
Thereafter, an Au electrode 9 is formed on an upper portion, and an AuGeNi electrode 10 having a window for extracting light is formed on a lower portion, and etching is performed in a cylindrical shape. The current flows through the reflection films 13 and 14 and the cladding layers 4 and 6, and is injected into the active layer 5.

[0003] Unlike the vertical cavity type laser, such a vertical cavity type laser has a thin active layer. Therefore, in order to amplify and oscillate light, it is necessary to increase the reflectivity of the reflective layer with high accuracy. Therefore, two kinds of substances having a large difference in the refractive index, for example, GaAs and AlAs, which are alternately grown with a thickness of ４ of the wavelength in the medium, are used as the semiconductor multilayer reflective films 13 and 14.

[0004]

In the semiconductor multilayer reflective film having the above-described structure, it is necessary to alternately stack materials having a large difference in refractive index, and therefore, it is necessary to select materials having greatly different band gaps. However, when substances with different band gaps are grown alternately, spikes occur in the bands due to discontinuity of the bands at the hetero interface,
It is a barrier to carriers. For this reason, the electric resistance in the semiconductor multilayer film portion becomes extremely high, and current injection is difficult.

At this time, a band diagram (bias voltage = O) in the n-GaAs, n-AlAs semiconductor multilayer film portion
V) is shown in FIG. Since the Fermi level 18 is constant in the semiconductor, a spike 19 occurs in the conduction band 15 at the heterojunction. Bias voltage (+ on right side)
FIG. 4 shows a band diagram when is applied. Here, the narrow gap semiconductor (GaAs) is reverse-biased at the hetero interface on the minus side with respect to the wide gap semiconductor (AlAs), and the spike 17 there is increased. This spike serves as a barrier to electrons, and the resistance value increases. Although the spike 20 remains on the forward bias side, it is much smaller than that on the reverse bias side. The height of the spike is mainly determined by the difference between the electron affinity of GaAs and AlAs and the magnitude of the bias voltage V. The width of the spike depends on the doping concentration and the dielectric constant ε of the semiconductor on both sides.
When the entire ^body is doped with 1.5 × 10 ¹⁷ cm ⁻³ , the spike width when the bias voltage is OV is about 200.
A (angstrom).

The same can be said for a p-type semiconductor multilayer film portion. When a bias voltage is applied, a spike occurs in a portion which is joined to a narrow gap semiconductor on the + side of a wide gap semiconductor portion.

In order to reduce the resistance by controlling the band spike, it is effective to dope the multi-layered film with a high concentration to increase the tunnel current. However, high-concentration doping at the time of crystal growth has problems of crystallinity and surface morphology, and there is a limit to the concentration. Particularly, high-concentration doping is difficult for bulk AlAs.
The limit was about 5 × 10 ¹⁷ cm ^{-3 for} n-type.

As another method of lowering the resistance, a method of grading the change in the composition of the hetero interface to reduce the spikes of the band and lower the resistance is also conceivable. However, in order to produce a graded layer at the time of growth, the growth temperature must be changed in a very small cycle, resulting in a problem that the number of steps is significantly increased and the yield is reduced.

An object of the present invention is to solve the conventional problems and to provide a semiconductor multilayer reflective film having low resistance and high reflectivity.

[0010]

According to the present invention, there is provided a semiconductor multilayer reflective film comprising two kinds of semiconductors of the same conductivity type having different refractive indices and band gap energies alternately having a thickness of a quarter of the wavelength in a medium. A semiconductor multilayer film formed; and an electrode portion for applying a bias voltage to the semiconductor multilayer film, wherein the conductivity type is n.
If the conductivity type is p-type, it is near the hetero interface on the negative side of the bias voltage in the wide band gap semiconductor of the semiconductor. It is characterized by having a δ-function high-concentration impurity doping region having a width of about several atomic layers near the interface.

Alternatively, a semiconductor multilayer reflective film of a surface emitting device such as a vertical cavity type surface emitting semiconductor laser, a surface emitting type LED, or a super radiant LED, which has the same conductivity type but different refractive index and band gap energy. And a pair of semiconductor multilayer films sandwiching an active layer, and an electrode section for applying a bias voltage to the semiconductor multilayer film, wherein the semiconductor layers are formed alternately with a thickness of a quarter of the wavelength in the medium. The semiconductor multilayer film has a different conductivity type, and is near the hetero-interface of the negative side of the bias voltage in the wide band gap semiconductor of the semiconductor multilayer film of the n-type conductivity or the wide width of the semiconductor multilayer film of the p-type conductivity. In the gap semiconductor, near the hetero-interface on the + side of the bias voltage, or both, a δ-functional high-concentration impurity-doped region having a width of several atomic layers is provided. Characterized in that it.

[0012]

According to the semiconductor multilayer reflective film of the present invention, the carrier is supplied and the width of the spike can be reduced by performing high concentration doping near the hetero interface. Further, since high-concentration doping is performed with a narrow width in the δ function, deterioration in crystallinity can be reduced. Moreover, if the film thickness is controlled, the optical reflectance does not deteriorate. As a result, a semiconductor multilayer reflective film having low resistance and high reflectivity can be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a surface emitting laser to which an embodiment of the present invention is applied to which a semiconductor multilayer reflective film of the present invention is applied.

A method for manufacturing this surface emitting laser will be described below. On the n-type GaAs substrate 1, 20 layers of n-GaAs2 and n-AlAs3 are alternately stacked as the n-type multilayer reflection film 13. At this time, the lower portion of the n-AlAs (the bias voltage −
1) from the interface with n-GaAs on the side of 20A
An n-type high-concentration doping region 11 is formed at a concentration of 10 ¹³ cm ^-2 and having a width of about several atomic layers (here, 20 A) in terms of a δ function. An n-type Al _0.3 Ga _0.7 As clad layer 4 is grown as a phase control layer on the n-type multilayer reflective film 13. Further, as an active layer, i-In _0.2 Ga having a thickness of 100 A is used.
_{A 0.8} As layer 5 is grown. Thereafter, a p-type Al _0.3 Ga _0.7 As clad layer 6 is further grown as a phase control layer,
On top of that, a p-AlA
15 layers of s7 and p-GaAs8 are alternately laminated. At this time, the p-type high-concentration doping region 12 is formed to have a width of 20 A in a δ function at a concentration of 1 × 10 ¹³ cm ⁻² at a portion of 20 A from the upper interface (+ side of the bias voltage) in p-AlAs. Formed. The above crystal growth is based on molecular beam epitaxy (MB
This was performed using the E) method. An Au electrode 9 is formed on an upper portion, and an AuGeNi electrode 10 having a window for extracting light is formed on a lower portion. Thus, the device of this example was completed.

FIG. 2A shows an energy band diagram of the n-type semiconductor multilayer reflective film portion having such a structure when no bias is applied, and FIG. 2B shows a case where a bias is applied. n-type high concentration impurity doping region 11
Is formed, the width of the spike 16 on the conduction band 15 can be made very narrow, that is, about 20A. As a result, the tunnel current is increased and the resistance is reduced as compared with the spike 17 (FIG. 4) in the case where the δ-functional high-concentration doping is not performed, and the current injection becomes easy.

In this embodiment, the high-concentration doping region is placed at 20 A from the hetero interface, but if it is within the range of 0 to 100 A, the resistance can be reduced as compared with the conventional case. Further, in this embodiment, the high-concentration doping regions are provided in the reflection films on both sides of p and n, but only one of the reflection films is effective. In addition, although it is placed in the entire reflection film, even if it is placed in only a part, the effect of reducing the resistance is obtained.

In the above embodiment, the semiconductor multilayer film is a reflection film in a surface emitting laser. However, the present invention is not limited to this, and the present invention can be applied to other semiconductor multilayer reflection films of devices requiring current injection. For example, a surface-emitting device in which the reflectance of a reflective film is changed to a super-radiant type LED, or a surface-emitting LED in which a reflective film is formed on a side opposite to a light extraction surface to increase light extraction efficiency, The present invention can also be applied to a pnpn-type surface emitting element and a switching element.

[0018]

As described above, according to the present invention, it is possible to reduce the series resistance of the multilayer reflective film portion without deteriorating the optical characteristics. A semiconductor multilayer reflective film useful for a surface optical device such as a laser can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a surface emitting laser according to an embodiment of the present invention.

FIG. 2 is an energy band diagram of a multilayer film according to one embodiment of the present invention.

FIG. 3 is a band diagram of a normal GaAs and AlAs multilayer film portion.

FIG. 4 is a band diagram when a bias voltage is applied to the multilayer film of FIG.

FIG. 5 is a sectional view of a conventional surface emitting laser.

[Explanation of symbols]

Reference Signs List 1 n-type GaAs substrate 2 n-GaAs 3 n-AlAs 4 n-type Al _0.3 Ga _0.7 As clad layer 5 In _0.2 Ga _0.8 As active layer 6 p-type Al _0.3 Ga _0.7 As clad layer 7 p-AlAs 8 p-GaAs 9 Au electrode 10 AuGeNi electrode 11 n-type high concentration doping region 12 p-type high concentration doping region 13 n-type semiconductor multilayer reflection film 14 p-type semiconductor multilayer reflection film 15 conduction band 16 spike when n-type high concentration doping 17 normal Reverse spike in the heterojunction of 18 Fermi level 19 Spike when the bias in the normal heterojunction is 0 20 Spike in the forward bias in the normal heterojunction 21 Valence band

Claims (2)

(57) [Claims] 1. A semiconductor multilayer film in which two types of semiconductors of the same conductivity type having different refractive indices and band gap energies are alternately formed with a thickness of a quarter of the wavelength in a medium, and a bias is applied to the semiconductor multilayer film. An electrode portion for applying a voltage, wherein the conductivity type is n-type, near the hetero-interface on the negative side of the bias voltage in the wide band gap semiconductor of the semiconductor, and when the conductivity type is p-type. Is + (plus) of the bias voltage in the wide gap semiconductor of the semiconductor.
Characterized in that it has a δ (delta) function high-concentration impurity doping region having a width of about several atomic layers near the hetero interface on the side of the semiconductor multilayer reflection film. 2. A semiconductor multilayer reflective film of a surface emitting device, wherein two types of semiconductors of the same conductivity type having different refractive indices and band gap energies are alternately formed with a thickness of 分 の of the wavelength in the medium. A pair of semiconductor multilayer films sandwiching an active layer, and an electrode portion for applying a bias voltage to the semiconductor multilayer films, wherein the pair of semiconductor multilayer films have different conductivity types, and a wide type of n-type semiconductor multilayer film. In the vicinity of the hetero interface on the negative side of the bias voltage in the bandgap semiconductor, or near the hetero interface on the positive side of the bias voltage in the wide gap semiconductor of the p-type semiconductor multilayer film, or both. A semiconductor multi-layer reflective film having a δ-function high-concentration impurity-doped region having a width of about several atomic layers.