Semiconductor light emission system

Abstract: A semiconductor light emission system, comprising a semiconductor laser part constituted of a second conductive current strictured layer with a striped groove perforated therein, a first conductive clad layer, a first or second conductive active layer, a second conductive clad layer on a first conductive substrate, and a second conductive - first conductive - second conductive bipolar transistor part constituted of said second conductive current strictured layer, first conductive clad layer, first or second conductive active layer, second conductive active layer in a position other than the semiconductor laser part.

Description: The present invention relates to a semiconductor light emission system, and is particulary concerned with a semiconductor laser capable of controlling a radiant power on a small current. Fig. 7 is a characteristic curve representing one example of current vs. radiant power characteristic according to a conventional semiconductor light emission system, and Fig. 8 is a sectional perspective diagram representing a prior art semiconductor light emission mentioned, for example, in Japanese Patent Laid-Open No. 192380/1985. In Fig. 7, the quadrature axis indicates an operating current, and the axis of ordinate indicates the radiant power. In Fig. 8, (1) denotes a first conductive (p-type or hereinafter referred to as "p-") GaAs substrate, (2) denotes a p-Aℓ ⊘.45 Ga ⊘.55 As buffer layer, (3) denotes a second conductive (n-type or hereinafter referred to as "n-") GaAs current block layer which is a current strictured layer with a striped groove provided on the p-GaAs substrate (1), (4) denotes a p-Aℓ ⊘.45 Ga ⊘.55 As lower clad layer, (5) denotes a p-type or n-type Aℓ ⊘.15 Ga ⊘.85 As active layer, (6) denotes an n-Aℓ ⊘.45 Ga ⊘.55 As upper clad layer, (7) denotes an n-GaAs contact layer, (8) denotes a p side electrode, and (9) denotes an n side electrode. A function of the prior art semiconductor light emission system will be described with reference to Fig. 7 and Fig. 8. When a positive voltage is applied on the p side electrode (8) and a negative voltage on the n side electrode (9), a junction between the n-GaAs block layer (3) and the p-Aℓ ⊘.45 Ga ⊘.55 As lower clad layer (4) becomes inverted of bias in a domain where the n-GaAs block layer (3) is present between the electrodes (8), (9), therefore a current does not flow therein, and the current flows in concentration only in the opening of a striped groove (5a) or thereabout. In this case, a hole is injected into a portion near a bottom of the striped groove (5a) of the Aℓ ⊘.15 Ga ⊘.85 As active layer (5) from the p-Aℓ ⊘.45 Ga ⊘.55 As lower clad layer (4), an electron is injected then from the n-Aℓ ⊘.45 Ga ⊘.55 As upper clad layer (6), and thus a light is emitted through a recombination of both the two. According as the injected current level is further raised, stimulated emission begins, as shown in the characteristic curve of Fig. 7, and it leads to a laser oscillation. The threshold current for laser oscillation will be 20 to 30 mA in the case of the semiconductor light emission system of Fig. 8, and an operating current for obtaining a 3mW radiant power is required at 40 mA or so. The prior art semiconductor light emission system has the above-described construction, and hence when the radiant power is to be controlled, the laser driving current must be controlled direct, and since the driving current is large running from several tens mA to several hundreds mA, the problem is that a control circuit becomes inevitably complicated. The invention has been done in view of the circumstances mentioned above, and its object is to provide a semiconductor light emission system capable of controlling a radiant power by a small current. In order to attain the aforementioned object, the invention comprises a semiconductor laser part and an annexed transistor part as disclosed in claim 1. The invention further comprises a semiconductor laser part and an annexed transistor part as disclosed in claim 4. In the bipolar transistor part according to the invention, an emitter current is controlled by the current injected into a base, a current injected into the semiconductor laser part is controlled consequently, and thus a radiant power is controlled thereby. As described above, the invention comprises forming a bipolar transistor part according to claims 1 or 4, annexed to the semiconductor laser part, therefore the current flowing to the semiconductor laser part can be controlled by the current injected into the base of the bipolar transistor part, thus ensuring an effect in controlling a radiant power by a small current. Fig. 1 is a side sectional view representing preferred embodiments (A) and (B) of a semiconductor light emission system according to the invention; Fig. 2 is a side sectional view representing embodiments (C) and (D) of a semiconductor light emission system not forming part of the invention as claimed Fig. 3 is a circuit diagram showing a simplified equivalent circuit of the embodiment (A) of Fig. 1 or the embodiment (D) of Fig. 2; Fig. 4 is a circuit diagram showing a semiconductor light emission system driving circuit when the system of Fig. 3 is used; Fig. 5 is a circuit diagram showing a simplified equivalent circuit of the embodiment (B) of Fig. 1 or the embodiment (C) of Fig. 2; Fig. 6 is a circuit diagram showing a semiconductor light emission system driving circuit when the system of Fig. 5 is used; Fig. 7 is a characteristic curve representing one example of current vs. radiant power characteristic according to a conventional semiconductor light emission system; Fig. 8 is a sectional perspective view showing an example of the prior art semiconductor light emission system. Embodiments (A) and (B) of the invention will now be described with reference to the accompanying drawings. Fig. 1 and Fig. 3 to Fig. 6 are drawings representing the embodiments of the invention, wherein Fig. 1 is a side sectional view representing the embodiments (A) and (B) of a semiconductor light emission system, Fig. 3 is a circuit diagram showing a simplified equivalent circuit of the embodiment (A) of Fig. 1 or the embodiment (D) of Fig. 2, Fig. 4 is a circuit diagram showing a semiconductor light emission system driving circuit when the system of Fig. 3 is used, Fig. 5 is a circuit diagram showing a simplified equivalent circuit of the embodiment (B) of Fig. 1 or the embodiment (C) of Fig. 2, and Fig. 6 is a circuit diagram showing a semiconductor light emission system driving circuit when the system of Fig. 5 is used. In Fig. 1, (10) denotes an n-block layer electrode connected to the n-GaAs block layer (3) working as a current strictured layer, (11) denotes a p-clad layer electrode connected to the p-AℓGaAs lower clad layer (4), (12) denotes a semiconductor laser part comprising the p-GaAs substrate (1), the p-AℓGaAs buffer layer (2), the n-GaAs block layer (3) working as a current strictured layer, the p-AℓGaAs lower clad layer (4), the p- or n-type doped AℓGaAs active layer (5), the n-AℓGaAs upper clad layer (6), and the n-GaAs contact layer (7), (13) denotes a bipolar transistor part described hereinlater, (14) denotes a current path flowing into the semiconductor laser part (12) which will be described hereinlater, (15) denotes a current path flowing into the bipolar transistor part (13) which will be described hereinlater, (T₁) denotes a terminal connected with the n side electrode (9), (T₂) denotes a terminal of the p-clad layer electrode (11), (T₃) denotes a terminal of the n-block layer electrode (10), and (T₄) denotes a terminal connected with the p side electrode (8). In Fig. 1, like reference characters represent like or corresponding components in the aforementioned example, and hence a repeated description will be omitted. In Fig. 2, (3a) denotes a p-GaAs block layer working as a current strictured layer with a striped groove provided thereon, (6a) denotes a first n-AℓGaAs upper clad layer as a first clad layer, (6b) denotes a second n-AℓGaAs upper clad layer as a second clad layer, (12) denotes a semiconductor laser part comprising the p-GaAs substrate (1), the p-AℓGaAs lower clad layer (4), the p- or n-type doped AℓGaAs active layer (5), the first n-AℓGaAs upper clad layer (6a), the p-GaAs block layer (3a) as a current strictured layer, the second n-AℓGaAs clad layer (6b), and the n-GaAs contact layer (7), and (13) denotes a bipolar transistor part constructed as described hereinlater. Then, in Fig. 1, the n-GaAs block layer (3) is formed between the p-AℓGaAs buffer layer (2) and the p-AℓGaAs lower clad layer (4), however, Fig. 2 indicates a construction wherein the p-GaAs block layer (3a) is present on the first n-AℓGaAs upper clad layer (6a). In Fig. 2 to Fig. 6, like reference characters represent like or corresponding components in Fig. 1, and hence a repeated description will be omitted. Next, the embodiments (A) to (D) will be described each with reference to Fig. 1 to Fig. 6. In the first place, the embodiment (A) of the invention will be taken up for description with reference to Fig. 1, Fig. 3 and Fig. 4. The embodiment (A) comprises the semiconductor laser part (12) and the bipolar transistor part (13) of Fig. 1, the semiconductor laser part (12) being the same in construction as the semiconductor light emission system in Fig. 8, and hence the repeated description will be omitted here. The bipolar transistor part (13) comprises the undoped AℓGaAs active layer (5), the n-AℓGaAs upper clad layer (6), the n-GaAs contact layer (7) which is an emitter of the bipolar transistor part (13), the n side electrode (9) which is an emitter electrode of the transistor, the p-AℓGaAs lower clad layer (4) which is a base of the transistor, the p-clad electrode (11) which is a base electrode of the transistor, the n-GaAs block layer (3) which is a collector of the transistor, and the n-block electrode (10) which is a collector electrode of the transistor, thus constituting the bipolar npn transistor (13). Next, an operation of the embodiment (A) will be described according to the drawing. An operation of each of the layers (1) to (7) of the semiconductor laser part (12) is equivalent to the above-described example, therefore the description will be omitted. The bipolar transistor part (13) operates as an npn bipolar transistor of the emitter, the emitter electrode, the base, the base electrode, the collector, and the collector electrode. The operation will further be described with reference to the circuit diagram of Fig. 3 and Fig. 4. As described above, an emitter corresponding domain in the bipolar transistor part (13) is common to the n-GaAs contact layer (7) and the n-AℓGaAs upper clad layer (6) of the semiconductor laser part (12), therefore a simplified equivalent circuit of the embodiment (A) will be as shown in Fig. 3, and the system of Fig. 3 will be realized as shown in Fig. 4 when connected through a circuit configuration. In the circuit of Fig. 4, a steady-state current (I) by a constant current source (16) flows between the terminal (T₁) and an earth (E). Further, a controlling current (IB) by an alternating current signal source (17) is injected in the p-AℓGaAs lower clad layer (4) at a portion corresponding to the base of the bipolar transistor part (13). In the circuit configuration of Fig. 4, the bipolar transistor part (13) is a common-collector transistor circuit, and a current I tr flowing from the collector to the emitter can be controlled by a small change of the base current (IB). The current I tr corresponds to a current, in Fig. 1, injected from the n-block layer electrode (10) and flowing out to an external circuit by way of the n-block layer (3), the p-lower clad layer (4), the active layer (5), the n-upper clad layer (6), the n-contact layer (7) and the n side electrode (9). The current path is indicated by the path (15) of Fig. 1. In the circuit shown in Fig. 4, a gross current (I) flowing to the semiconductor laser part (12) or the system according to the invention and to the bipolar transistor part (13) is constant, and the current (I) is expressed by the sum of a current (I LD ) flowing to the semiconductor laser part (12) and a current (I tr ) flowing out of the emitter of the bipolar transistor part (13). Accordingly, the current (I LD ) flowing to the semiconductor laser part (12) (or the current flowing through the path (14) of Fig. 1) will be: I LD = I - I tr = I - f(IB) Here, f(IB) represents a function of the current (IB). Generally, an operating current of the laser and a radiant power are correlated as indicated in Fig. 7, and when the current exceeds a threshold necessary for oscillation, the relation between the radiant power and the current becomes almost linear. Accordingly, the radiant power can be controlled by the small current (IB) injected from the p-clad layer electrode (11) corresponding to the base electrode from the aforementioned expression (1) in the system. The embodiment (B) of the invention will be described next with reference to Fig. 1, Fig. 5 and Fig. 6. The embodiment (B) comprises the semiconductor laser part (12) and the bipolar transistor part (13) of Fig. 1, of which the semiconductor laser part (12) is the same in construction as the embodiment (A) described above, and the description will be omitted consequently. In Fig. 1, the bipolar transistor part (13) constitues a pnp bipolar transistor with the p-AℓGaAs lower clad layer (4) as a p-collector, the n-GaAs block layer (3) as an n-base, the p-AℓGaAs buffer layer (2) and the p-GaAs substrate (1) as a p-emitter. In this case, a film thickness of each layer varies from the above-described embodiment (A). As mentioned hereinbefore, the p-emitter corresponding domain of the bipolar transistor (13) is common to the p-AℓGaAs buffer layer (2) and the p-GaAs substrate (1) of the semiconductor laser part (12), therefore a simplified equivalent circuit of the embodiment (B) will be as shown in Fig. 5. A semiconductor light emission system driving circuit when the embodiment (B) shown in the circuit diagram of Fig. 5 is used is shown in Fig. 6. An operation in this case may apply corresponding to the embodiment (A) described hereinabove, therefore a repeated description will be omitted. In the embodiment (B), the radiant power can also be controlled by a small current injected from the n-block layer electrode (10) corresponding to a base electrode as in the case of embodiment (A). The embodiment (C) will be described next with reference to Fig. 2, Fig. 5 and Fig. 6. The embodiment (C) comprises the semiconductor laser part (12) and the bipolar transistor part (13) of Fig. 2, of which the semiconductor laser part (12) is constituted, as described in Fig. 2, of the p-GaAs substrate (1), the p-AℓGaAs lower clad layer (4), the p or n-type doped AℓGaAs active layer (5), the first n-AℓGaAs upper clad layer (6a), the p-GaAs block layer (3a), the second n-AℓGaAs upper clad layer (6b), the n-GaAs contact layer (7) and the bipolar transistor part (13) is constituted as a pnp bipolar transistor comprising the p-GaAs substrate (1), the p-AℓGaAs lower clad layer (4), the p or n-type doped AℓGaAs active layer (5), the first n-AℓGaAs upper clad layer (6a) and the p-GaAs block layer (3a). A simplified equivalent circuit of the embodiment (C) is equivalent to Fig. 5, and the semiconductor light emission system driving circuit is equivalent to Fig. 6. Since an operation of the embodiment (C) applies correspondingly to the above-described embodiment (A), no further description will be given repeatedly thereon. In the embodiment (C), the radiant power can be controlled also by a small current injected from the first n-upper clad layer electrode (10) corresponding to a base electrode as in the case of embodiment (A). Next, the embodiment (D) will be described with reference to Fig. 2, Fig. 3 and Fig. 4. The embodiment (D) comprises the semiconductor laser part (12) and the bipolar transistor part (13) of Fig. 2, of which the semiconductor laser part (12) is similar to the semiconductor laser part (12) of the above-described embodiment (C), therefore the description will be omitted. The bipolar transistor part (13) is constituted as an npn bipolar transistor comprising the first n-AℓGaAs upper clad layer (6a), the p-GaAs block layer (3a), the second n-AℓGaAs upper clad layer (6b) and the n-GaAs contact layer (7). A simplified equivalent circuit of the embodiment (D) is equivalent to Fig. 3, and the semiconductor light emission system driving circuit is similar to Fig. 4. An operation of the embodiment (D) applies correspondingly to the embodiment (A) described hereinabove, therefore a repeated description will be omitted. In the embodiment (D), the radiant power can also be controlled by a small current injection from the p-block layer electrode (11) corresponding to a base electrode as in the case of embodiment (A). Further, the embodiments (A) and (B) of the invention indicate the case where each semiconductor is formed of an AℓGaAs group material, however, a similar effect will also be obtainable from forming of an InGaAs group material.

Claims: A semiconductor light emission system, comprising a semiconductor laser part (12) constituted of a second conductive type current strictured layer (3) with a striped groove perforated therein, a first conductive type clad layer (4), a first or second conductive type active layer (5), a second conductive type clad layer on a first conductive type substrate (1), and an annexed second conductive type - first conductive type - second conductive type bipolar transistor part (13) constituted of electrically and physically common parts of said second conductive type current strictured layer (3), first conductive type clad layer (4), first or second conductive type active layer (5), second conductive type clad layer (6). The semiconductive light emission system as defined in claim 1, the semiconductor being constituted of an AℓGaAs material. The semiconductor light emission system as defined in claim 1, the semiconductor being constituted of an InGaAs material. A semiconductor light emission system, comprising a semiconductor laser part (12) constituted of a second conductive type current strictured layer (3) with a striped groove perforated therein, a first conductive type clad layer (4), a first or second conductive type active layer (5), a second conductive type clad layer (6) on a first conductive type substrate (1), and an annexed first conductive type - second conductive type - first conductive type bipolar transistor part (13) constituted of electrically and physically common parts of said first conductive type substrate (1), second conductive type current strictured layer (3), first conductive type clad layer (4). The semiconductor light emission system as defined in claim 4, the semiconductor being constituted of an AℓGaAs material. The semiconductor light emission system as defined in claim 4, the semiconductor being constituted of an InGaAs material.

Inventors: HIRONAKA MISAO KOYA HIRATA KYO, YAGI TETSUYA C O MITSUBISHI DE, HIRONAKA, MISAO, KOYA HIRATA KYODO JUTAKA NO. 233, YAGI, TETSUYA, Yagi, Tetsuya, c/o Mitsubishi Denki Kabushiki K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: H01S3
IPC codes: H01S5