JPH0478036B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to a semiconductor light emitting device, and in particular, to a semiconductor light emitting device, which has a single oscillation mode in the axial and lateral directions, has a low threshold current, has high efficiency, and is capable of increasing output. The present invention relates to a suitable surface emitting semiconductor laser.

(b) Background of the Technology Laser light is being applied to optical fiber communications, various industrial fields, and consumer equipment. Various types of lasers are selected and used in these fields depending on the purpose, but semiconductor lasers have the advantage of being able to control their oscillation wavelength, being compact and suitable for mass production, and achieving high efficiency simply by passing a current through them. It has the most future potential due to its features such as ease of use for oscillation, realization of the required wavelength band, stable single transverse and axial mode oscillation, improvement of current-light output characteristics, and optical beam Many efforts have been made to improve various characteristics such as reducing the divergence angle and increasing the output power.

(c) Prior art and problems A number of semiconductor laser structures have been proposed to date to achieve the above objectives, but most of them are fabricated by fabricating a Fabry-Perot optical cavity by cleaving a semiconductor crystal, etc. It is a structure that forms.

This end face formation by cleavage restricts the shape and dimensions of the laser chip, making it difficult to shorten the cavity length and control the axial mode, and also making it difficult to form an integrated circuit including the laser.

A surface emitting laser is known as one type of semiconductor laser that addresses these problems. A surface-emitting laser is a semiconductor laser that emits laser light in a direction perpendicular to the main surface of a semiconductor substrate.
A Perot optical resonator is constructed using the surface of an epitaxially grown crystal as a reflective surface.

Since the surface emitting laser has such a structure, (a)
It is easy to shorten the optical resonator length and it is possible to unify the axial mode. (b) It is easy to widen the light emission area, increase the light output, and narrow the light emission angle. (c) The configuration of a two-dimensional laser array is easy. (d) Suitable for the configuration of monolithic optical integrated circuits. It has excellent characteristics such as:

However, in conventional surface emitting lasers, due to this structure, (a) the resonant surface of the Fabry-Perot optical cavity is an epitaxially grown crystal surface, so it is difficult to form a mirror surface like a cleaved surface; It is difficult to achieve uniform resonance. (b) It is impossible to stabilize the transverse mode of oscillation. (c) Since the current is introduced in a direction parallel to the optical resonator, it is difficult to effectively increase the current density in the active region, and the conversion efficiency is low. It comes with drawbacks such as:

The above-mentioned excellent features of the surface emitting laser are features that are desired for future semiconductor lasers, and improvement of the above-mentioned drawbacks will have a great effect on the application field of semiconductor lasers.

(d) Purpose of the Invention The present invention provides a semiconductor light emitting device, particularly a surface emitting laser, which does not require a Fabry-Perot resonance surface, reduces threshold current, improves quantum efficiency, and unifies axial and transverse modes. The purpose is to provide a structure to be achieved.

(e) Structure of the Invention The object of the present invention is to provide a first semiconductor layer of a first conductivity type having a forbidden band width of Ea, a refractive index of n _a and a thickness of d _a , a forbidden band width of Ec, refractive index n _c and thickness d _c
and a second semiconductor layer of a first conductivity type that is stacked alternately, a light-emitting region that outputs light in a direction perpendicular to the first and second semiconductor layers, and a light-emitting region that outputs light in the vertical direction of the first and second semiconductor layers; Adjacent to the layer extending direction, the light emitting region and pn
and a second conductivity type semiconductor layer constituting a junction,
The forbidden band width and the refractive index in the light emitting region are Ea<Ec and n _a >n _c , the wavelength in vacuum of the emitted light λ _p , the effective refractive index n _e of the laminated structure of the light emitting region, and the positive The relationship of the integer l is achieved by approximately satisfying d _a +d _c =l·λ _p /(2n _e ), and the light emitting region and the semiconductor layer forming the pn junction with the light emitting region are of the second conductivity type. an opening that is commonly formed on a semiconductor substrate and that penetrates the semiconductor substrate to expose one end of the light emitting region; and an electrode formed on the surface of the semiconductor substrate and the other end of the light emitting region. This is achieved by having.

(f) Embodiments of the Invention The present invention will be specifically described below using embodiments with reference to the drawings.

The figure is a perspective view showing one piece obtained by dividing the embodiment of the present invention into two equal parts.

In the figure, 1 is an n-type gallium, arsenic (GaAs) substrate, 2 is an n-type gallium-aluminum-arsenic (Ga _0.7 Al _0.3 As) cladding layer, and 3 is an n-type
The GaAs active layer is formed by alternately laminating a cladding layer 2 and an active layer 3 as will be explained in detail later. 4 shown with diagonal lines is the cladding layer 2
5 is an insulating layer, 6 is an n-side electrode, and 7 is a p-side electrode.

In this example, GaAs constituting the active layer is
Layer 3 has a forbidden band width Ea = 1.42 [eV] and a refractive index for the peak wavelength of photoluminescence λp = 0.87 [μm].
n _a = 3.60, Ga _0.7 forming the cladding layer
The Al _0.3 As layer 2 has a forbidden band width Ec = 1.8 [eV] and the wavelength
The refractive index n _c = 3.39 for light of 0.87 [μm],
The relationship Ea<Ec, n _a > n _c is satisfied.

In addition, the thickness of each layer of the GaAs active layer 3 is d _a =0.15
[μm], Ga _0.7 Al _0.3 As cladding layer 2 is formed so that the thickness of each layer sandwiched between active layers 3 is d _e =0.225 [μm], so that d _a +d _e =0.375 [μm]. , and the GaAs active layer 3 and the Ga _0.7 Al _0.3 As cladding layer 2 for the vacuum wavelength λ _p = λ p = 0.87 [μm] of the emitted light.
The effective refractive index of the semiconductor laminated structure (the ratio β/k _O of the propagation constant β in the semiconductor laminated structure and the propagation constant k _p in vacuum) n _e = 3.48, Bragg's reflection condition d _a + d _e =lλ _p /2n _e is satisfied for l=3, and the GaAs active layer 3 is
20 layers of Ga _0.7 Al _0.3 As cladding layer 2 are formed alternately by molecular beam epitaxial growth in 21 layers, including the first and last two layers whose thickness is not restricted.
Note that the number N of layers in the GaAs active layer 3 is desirably about 10 or more, and a metal-organic chemical vapor deposition method or the like may be used as the growth method for these layers.

In this embodiment, in the laminated structure of the cladding layer 2 and the active layer 3 having the configuration described above, a cylindrical structure is added which penetrates from the cladding layer 2 in contact with the substrate 1 to the cladding layer 2 in contact with the insulating layer 5, as shown in the figure. The p-type region 4 is formed by, for example, diffusion of zinc (Zn).

Next, a layer of gold, for example, is deposited on the substrate 1 to form the n-side electrode 6.
After depositing the germanium/gold (AuGe/Au) film, an opening is provided through the AuGe/Au film and the substrate 1 to expose the first cladding layer 2, and selectively in contact with the last cladding layer 2. Then, an insulating film 5 exposed in the p-type region 4 and a p-side electrode 7 made of, for example, gold/zinc (AuZn) are formed.

In the laser of this embodiment having the structure described above, the current flowing from the p-side electrode 7 to the n-side electrode 6 is caused by electrons flowing from the n-type region 3 to the p-type region 4 in the GaAs layer 3 with a low built-in potential. The electrons are then injected, and radiative recombination occurs within the electron diffusion width (on the order of several μm).

Of the light generated here, the peak component whose wavelength in vacuum is λ _p becomes a oscillation state in which the longitudinal mode is matched to the interface due to the semiconductor stacked structure that satisfies Bragg's reflection condition. The laser beam is emitted from the aperture, as schematically shown by the arrow in the figure.

In particular, in the structure in which the pn junction of this embodiment has an endless annular shape, for example, the electron concentration in the n-type region is set to 5×
10 ¹⁸ [cm ^-3 ] or more, and the hole concentration in the p-type region is 8
By selecting the impurity concentration of both regions to be below ×10 ¹⁸ [cm ^-3 ], the refractive index of the p-type region 4 is made larger than the refractive index of the surrounding n-type region, thereby confining light. In addition, stabilization is achieved even in the transverse mode, and even a single mode is possible.

However, the transverse mode can be stabilized by diffusing acceptor impurities into the n-side semiconductor stack structure, as has already been done for semiconductor lasers with a transverse junction stripe structure.
By forming a p ₊ type region with a high concentration of about ×10 ²⁰ [cm ^-3 ] and then re-diffusing impurities to form a p type region with a high refractive index, refractive index guiding is formed. is also possible. If this type of refractive index guiding is provided, it is unnecessary for the pn junction to form an endless ring shape for guiding light, but it is suitable for practical use and is suitable for expanding the light emitting surface and integrating it. For the laser, it is advantageous to have a structure in which the pn junction is annular and light is confined within the junction interface, for example, as in the above embodiment.

Unlike conventional surface emitting lasers, the surface emitting laser of the present invention has a light emitting region that satisfies Bragg's reflection condition and is superimposed in multiple layers, so the threshold current is reduced.
And quantum efficiency is improved.

In the above embodiment, the pn junction is a homojunction, but for example, the semiconductor laminated structure is grown with its conductivity type as p-type, and after selective etching to leave a required p-type region, n-type GaAlAs is formed.
By selectively growing the active layer pn
Since the junction can be a heterojunction, carrier injection efficiency is improved.

Furthermore, in the above embodiment, the resonance condition is satisfied by making the sum of the active layer thickness d _a and the cladding layer thickness d _c equal to an integer multiple of λ ₀ /2n _e ; Almost the same effect can be obtained by making _{d a} sufficiently thinner than the cladding layer thickness d _c and making the cladding layer thickness d _e equal to an integral multiple of λ _p /2n _e . It is possible to obtain.

(g) Effects of the Invention As explained above, according to the present invention, the stability of the axial mode of a surface emitting laser is further improved than before, and it becomes easy to further expand the light emission area and increase the optical output. In addition, the transverse mode has been stabilized, the threshold current has been reduced, and the quantum efficiency has been improved, not only meeting the strong demands for semiconductor lasers but also achieving two
Of course, dimensional laser arrays make a major contribution to the realization of monolithic optical integrated circuits.

[Brief explanation of the drawing]

The drawing is a perspective view including a cross section of one piece obtained by dividing the semiconductor light emitting device according to the embodiment of the present invention into two. In the figure, 1 is an n-type GaAs substrate, 2 is an n-type
GaAlAs clad layer, 3 is n-type GaAs active layer, 4
is a p-type region, 5 is an insulating layer, 6 is an n-side electrode, and 7 is a p-type region.
The side electrode is shown.

Claims (1)

[Claims] 1. A first semiconductor layer of a first conductivity type having a forbidden band width of Ea, a refractive index of n _a and a thickness of d _a ;
Ec, a second semiconductor layer of the first conductivity type having a refractive index of _nc and a thickness of _dc are laminated alternately, and light is output in a direction perpendicular to the first and second semiconductor layers. a light emitting region adjacent to the first and second semiconductor layers in the extending direction;
a semiconductor layer of a second conductivity type forming a pn junction with the light emitting region, the forbidden band width and refractive index in the light emitting region are Ea<Ec and n _a >n _c , and the vacuum of the emitted light is wavelength λ _p in the middle, the effective refractive index of the laminated structure of the light emitting region
A semiconductor light emitting device characterized in that the relationship between n _e and a positive integer l satisfies approximately d _a +d _c =l·λ _p /(2n _e ). 2. The light emitting region and a semiconductor layer forming a pn junction with the light emitting region are formed on a semiconductor substrate of a second conductivity type, and penetrate through the semiconductor substrate to expose one end of the light emitting region. The semiconductor light emitting device according to claim 1, comprising an opening and an electrode formed on the surface of the semiconductor substrate and the other end of the light emitting region.