JPH0389583A - Algainp visible light semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce the electrons sensitive to a boundary and suppress the decrease of carrier lifetime in a semiconductor by growing a crystal without interruption with the ratio of V group element raw material and III group element raw material being made higher in the central part of an active layer. CONSTITUTION:In an active layer, the forbidden band width is smaller in the central part. This because the natural superlattice formation depends on the V/III ratio in AlGaInP or GaInP grown by MOVPE process and the forbidden band with is made smaller as the V/III ratio is increased. Therefore, there are four boundaries at which the energy is discontinuous. The MOVPE process is crystal growing process controlled by the III group element raw material, and the supplied amount of the V group element raw material has no influence on the crystal composition and irregularity of the supply of the V group element raw material has no influence on the crystal lattice. Therefore, the crystal property at the boundary 1 is scarcely different from the crystal property of the active layer as the bulk as long as the growth is not interrupted at the interface.

Description

[Detailed description of the invention] (Industrial application field) The present invention is Aj! GaI related.

nP visible light semiconductor laser (prior art) A semiconductor laser generally has a double heterostructure in which an active layer is sandwiched between cladding layers. Since the active layer and the cladding layer have different crystal compositions, there is some kind of discontinuity between the active layer and the cladding layer when the growth is interrupted during crystal growth, which affects the interface and causes implantation into the active layer. It is often said that this causes non-radiative recombination of released carriers, shortens carrier lifetime, etc., and deteriorates laser characteristics.

(Problems to be Solved by the Invention) The present invention provides an AlGaInP visible-light semiconductor laser manufactured by metal organic vapor phase epitaxy (hereinafter abbreviated as MOVPE), in which some of the crystals at the interface between the cladding layer and the active layer The present invention, which aims to improve non-radiative recombination of carriers or shortening of carrier lifetime caused by discontinuities, makes full use of the properties of AlGaInP crystal grown by MOVPE.

(Means for Solving the Problems) Means provided by the present invention to solve the above problems are as follows:
GaInP or AlGaInP crystal that becomes the active layer is M
An AlGaInP visible light semiconductor laser grown by the OVPE method, in which the central part of the active layer is made of a group V element raw material.
The crystal is grown by increasing the ratio (hereinafter abbreviated as V1m ratio) to the group element raw material without interrupting crystal growth.

(effect) Hereinafter, the operation of the present invention will be explained using the drawings.

FIG. 1 shows a band diagram of the A4GaInP visible light semiconductor laser of the present invention. FIG. 1 is a band diagram in a light emitting state in which the conductivity type of the active layer is P type and the semiconductor laser is forward biased. In the active layer, the forbidden band width becomes small in the central part. This is MOV
AIG@InP or G crystal grown by PE method
This is because in aInP, the formation of a natural superlattice depends on the v/■ ratio, and the forbidden band width becomes smaller as the V/I ratio increases. Therefore, there are four planes where the energy is discontinuous. The discontinuous surface that occurs inside the active layer is called interface 1.
, the interface between the active layer and the cladding layer is defined as interface 2. First, the difference between interface 1 and interface 2 will be explained from the viewpoint of crystal growth.

The MOVPE method is a crystal growth method that is governed by group V element raw materials, and the supply amount of group V element raw materials does not affect the crystal composition, and irregularities in the supply of group V element raw materials, apart from group V vacancies, affect the crystal composition. There is no effect on the lattice, so the crystallinity at the interface 1 is almost the same as the bulk crystallinity of the active layer unless growth is interrupted at that interface.

On the other hand, interface 2 is an interface between the active layer and the cladding layer, and is an interface where the amount of group (2) supplied is varied. If it is necessary to interrupt the crystal growth at that time, more impurities than in the bulk may be mixed in at the interface, or irregularity in the supply of the group III element raw material immediately after switching the supply amount of the group III element raw material. Since the MOVPE method is based on the supply rule of group (Ⅰ) elements, this is directly reflected in the crystallinity at the interface and may worsen the crystallinity. This irregularity in supply can easily occur due to pressure fluctuations in the supply piping etc. due to switching. Therefore, it is difficult to maintain the same crystallinity at the interface 2 as in the bulk.

Most threading dislocations that occur during epitaxial growth occur from an interface equivalent to interface 2. In the present invention, there are two types of interfaces, but only one of them, interface 2, causes non-emission of carriers. All we have to do is discuss recombination.

Next, we will discuss the non-radiative recombination of carriers per unit time at the interface.

The rate of non-radiative recombination at an interface is proportional to the carrier density in the active layer in contact with the interface. Its non-radiative recombination rate is R
Then, Roen: carrier concentration.

Aj! according to the present invention! The carrier density n in a G@InP visible light semiconductor laser is given by the following equation. Only electrons will be explained here.

Here, ρC(E) is the density of states in the conduction band, f, (E) is the Fermi-Dirac distribution function, and EC is the energy at the bottom of the conduction band. ΔE and ΔE are quantities determined by the Fermi level of each semiconductor layer and the amount of band discontinuity in the conduction band and valence band. On the other hand, the active layer has a uniform V
Conventional Aj with crystal growth at /I ratio! The carrier density in a GaInP visible light semiconductor laser is given by, and in the case of the present invention, the carrier density is smaller, tR Simply stated, only electrons with energy greater than Ee + △E1 are recombined at the interface 2. It will contribute. Therefore, in the AlGaInP visible light semiconductor laser of the present invention, non-radiative recombination at the interface between the active layer and the CLA and RAD layers is reduced.

(Example) Next, the present invention will be explained in more detail with reference to Examples.

The created DH laser is (AN *, aG a *, s
) *, sIns, iP crystal as cladding layer, thickness 0
．． It has a double heterostructure with active layers of 1 μm of GaB, iIn*, and iP. In the example, the P Hs flow rate during growth of 0.06 μm at the center of the active layer was set to 40 μm.
When the active layer is grown to a thickness of 0.02 μm after the start of active layer growth and before the end of active layer growth, the pH5t amount is 70 sccm.
GaIn at a PHs flow rate of 70 sccm
The PL peak energy of P is 1.89 eV, and the PL peak energy of GstInP at a PH8 flow rate of 400 sccm is 1.84 eV, and the difference therebetween is about 50 m e V. When the laser was actually oscillated, it oscillated at a threshold current of about 60 mA, which was about 70 mA in a conventional device having an active layer of the same thickness formed at a constant flow rate of 400 sccm per PHs. Although it cannot be concluded that this difference in oscillation threshold is the effect explained in the (effect) column, it is considered as one of the effects.

(Effects of the invention) As explained in the (effect) section, it is possible to reduce the number of electrons that sense interfaces that have problems such as non-radiative recombination (electron wave function reaches the interface), It is possible to suppress the decrease in laser power life time.

In addition, in the examples, the supply of the group V element raw material is increased and decreased stepwise, but it may also be changed gradually.In this case, a clearly distinguished interface (corresponding to interface 1) in the active layer is used.
ceases to exist. In this respect as well, the essential difference between Interface 1 and Interface 2 explained in the (Operation) section becomes clear.

[Brief explanation of drawings]

FIG. 1 is a band diagram of the semiconductor laser of the present invention when emitting light.

Claims (1)

[Claims] GaInP formed by organometallic decomposition vapor phase growth method
Alternatively, it has a double heterostructure in which an active layer made of an AlGaInP semiconductor is sandwiched between cladding layers made of an AlGaInP semiconductor having a larger forbidden band width than the active layer, and the semiconductor thin film serving as the active layer has a certain level during its crystal growth process. 1. An AlGaInP visible light semiconductor laser, characterized in that the amount of Group V element raw material supplied is increased during central growth of the thin film while supplying Group III element raw material.