JPH0793473B2 - Optical semiconductor device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a surface-emitting type semiconductor laser device with an optical modulator.

[Conventional technology]

The surface-emitting type semiconductor laser device does not require the formation of a resonator by the cleavage plane because the emitting direction of the laser light is perpendicular to the substrate, and therefore, it is suitable for optoelectronic integrated circuits (OEICs) that require multi-functional integration. It is regarded as a promising semiconductor laser device. The structure of the surface-emitting type semiconductor laser device having such characteristics is, for example, as shown in FIG.
N type InP buffer layer (2), n type InP on P substrate (1)
Layer with a semiconductor multi-layered film composed of n-type GaInAsP layer (3), non-doped GaInAsP active layer (4), reflector with a semiconductor multi-layered film composed of p-type InP layer and p-type GaInAsP layer (5), p-type GaInAsP The contact layer (6) is sequentially formed, and finally the electrodes (6) and (7) are attached to the top and bottom. The longitudinal mode interval determined by the laser cavity length is inversely proportional to the cavity length. Therefore, in this structure, the cavity is as short as about 10 μm, so the longitudinal mode spacing is about 200 Å, which is a normal Fabry-Perot type semiconductor laser device (resonator length of about 300 μm).
m) and spread about 30 times, and stable single-mode oscillation can be obtained.

[Problems to be solved by the invention]

The light output of the surface-emitting type semiconductor laser device is stable single mode oscillation in high speed modulation. However, when the injected carrier density increases, the refractive index of the laser medium decreases due to the plasma effect, and the oscillation wavelength shifts to the short wavelength side. As described above, when the semiconductor laser device is directly modulated, there is a problem that a so-called chirping phenomenon occurs in which the oscillation wavelength changes with time.

The present invention has been made in consideration of the above points,
The purpose is to maintain single mode,
An object is to provide an optical semiconductor device with small chirping even during high-speed modulation.

[Means for solving problems]

To achieve the above object, according to the present invention, a first conductive type reflective layer having a multi-layer structure of a hetero semiconductor thin film on a first conductive type semiconductor substrate, an active layer, and a multi-layer structure of a hetero semiconductor thin film are provided. A surface emitting laser element portion formed by sequentially forming two conductive reflection layers; a semiconductor insulating layer that transmits laser light from the active layer on the second conductive reflection layer; An optical modulator configured by sequentially forming a conductive type or second conductive type semiconductor layer, an active layer having an emission wavelength equal to or shorter than that of the active layer, and a second conductive type or first conductive type semiconductor layer. An optical semiconductor device is provided which is characterized in that the surface emitting laser device section and the optical modulator section are independently driven.

By the way, when a high electric field is applied to the depletion layer of the pn junction, a band gap reduction phenomenon due to a high electric field called Franz-Keldysh effect occurs, and the light absorption coefficient has a skirt on the long wavelength side of light. Therefore, when a high electric field is applied to the junction, it becomes difficult for light to pass through on the long wavelength side.

In the optical semiconductor device of this structure, the surface-emitting laser device section is driven by DC current to continuously oscillate, a voltage is applied to the optical modulator section independently of that, and the voltage is changed to The absorption coefficient is changed to modulate the laser light. As a result, since the laser light is driven by a direct current, its wavelength is stable and no chirping occurs.

〔Example〕

 The present invention will be described below based on the embodiments shown in the drawings.

FIG. 1 is a sectional view of an essential part of an embodiment of an optical semiconductor device according to the present invention. On the n-type InP substrate (11), an n-type InP buffer layer (12), a reflector made of a semiconductor multilayer film (13) including an n-type InP layer and an n-type GaInAsP layer, a non-doped GaInAsP active layer (14), p -Type InP layer and p-type GaInAsP semiconductor multilayer film (15) reflecting mirror, p-type GaInAsP contact layer (1
6) is formed sequentially. By passing a direct current between the electrodes (17) and (18), continuous laser light with a wavelength of 1.3 μm can be obtained. Further, the GaInAsP contact layer (1
6) on top, via the InP insulating layer (19) for element isolation,
n-type InP layer (20), non-doped InP layer and non-doped GaInAs
A quantum well active layer (21) consisting of P, a p-type InP layer (22),
A p-type GaInAsP contact layer (23) is sequentially formed. In the active layer having the quantum well structure, the absorption coefficient at the wavelength position where laser oscillation occurs is extremely low. However, the electrode (2
When a voltage is applied between 3) and (24), the optical absorption coefficient of the quantum well active layer is tailed to the long wavelength side of light due to the energy gap reduction effect, and the laser layer is transmitted from the active layer (14). The rate will be low. Therefore, the output light can be modulated by modulating the voltage applied between the electrodes (23) and (24). The element having the structure shown in this embodiment can be manufactured by a metal organic chemical vapor deposition (MOCVD) method which has good controllability of film thickness and enables growth of an extremely thin film.

Although the oscillation wavelength of this embodiment is 1.3 μm, a desired wavelength of 1.1 to 1.6 μm can be obtained by changing the material of the active layer. Moreover, the threshold current can be lowered by making the structure an embedded type.

〔The invention's effect〕

As described above, according to the present invention, since the surface-emitting type semiconductor laser device section and the optical modulator section are separated from each other, there is almost no change in the refractive index of the laser-mediated portion, and the wavelength charg- er can be maintained even during high-speed modulation. The ping can be made smaller than that during direct modulation, and since it is a surface emitting type, stable single wavelength operation can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an optical semiconductor device according to the present invention, and FIG. 2 is a sectional view of an essential part of a conventional surface-emitting type semiconductor laser device. 1,11 …… n-type InP substrate, 2,12 …… n-type InP buffer layer, 3,
13 …… Semiconductor multilayer film consisting of n-type InP layer and n-type GaInAsP layer, 4,14 …… Non-doped GaInAsP active layer, 5,15 …… p-type I
Semiconductor multilayer film consisting of nP layer and p-type GaInAsP layer, 6,16 ...
p-type GaInAsP contact layer, 7,8,17,18,24,25 ... Electrode,
19 …… InP insulating layer, 20 …… n-type InP layer, 21 …… Undoped
Quantum well active layer consisting of InP layer and non-doped GaInAsP layer, 22 ... p-type InP layer, 23 ... p-type GaInAsP contact layer.

Claims (1)

[Claims] 1. A first-conductivity-type reflective layer having a multi-layer structure of a hetero semiconductor thin film, an active layer, and a first-conductivity-type semiconductor substrate,
A surface-emitting type laser element portion formed by sequentially forming a second conductive type reflective layer having a multilayer structure of a hetero semiconductor thin film, and a laser beam from the active layer on the second conductive type reflective layer. A semiconductor insulating layer that is transparent to the first conductivity type or the second conductivity type
A conductive type semiconductor layer, an active layer having an emission wavelength equal to or shorter than that of the active layer, and an optical modulator configured by sequentially forming a second conductive type or a first conductive type semiconductor layer,
An optical semiconductor device characterized in that a surface emitting laser device section and an optical modulator section are independently driven.