JP2940831B2 - p-type II-VI compound semiconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a p-n using a II-VI compound semiconductor (including a ternary or higher solid solution) having a high energy band gap (Eg.gtoreq.2.3 eV).
The present invention relates to a high-quality p-type II-VI group compound semiconductor required for manufacturing a visible short-wavelength (540 nm or shorter) light-emitting element having a junction.

[0002]

2. Description of the Related Art In II-VI group compound semiconductors (ZnSe, ZnS, CdS, and solid solutions thereof) for visible and short wavelength light emitting devices, conventional lithium (Li), nitrogen (N),
Attempts have been made to form a p-type conductive layer by adding oxygen (O). However, among these impurities, Li easily moved in the crystal, and the electrical characteristics of the crystal to which Li was added were unstable. Also, the addition of nitrogen or oxygen induces large strain in the crystal lattice, which tends to cause defects and easily cause electrical compensation. The activation rate is extremely low, less than several percent, and the reproducibility and reliability are high. She was poor in sex. Therefore, by adding any of these three types of acceptor impurities, it is impossible to produce a p-type conductive crystal layer having a carrier concentration of 10 ¹⁷ cm ⁻³ or more required for producing a practical pn-type light-emitting element with good reproducibility. It was difficult.

[0003]

Conventionally, carrier (electron or hole) concentration control of Si, Ge and a compound semiconductor is performed by adding an impurity atom called a donor (or acceptor) to a base crystal. . Taking an acceptor atom for Si as an example, a group III atom (boron, aluminum, etc.) having one less valence number than Si for valence electron 4 is used. A group I atom (such as lithium or sodium) or a group V atom (such as nitrogen or phosphorus) is added to ZnSe, which is one of the target materials of the present invention, as an acceptor atom. The acceptor atom is selected to have one (or two) fewer valence electrons than the number of valence electrons of the atoms constituting the host crystal, and these are referred to as "valence electron-controlled acceptors". The above-mentioned valence-electron-control-type acceptor is composed of Si and Ge, which are perfect covalent crystals, and III-V compound semiconductors such as GaAs and InP, which have most covalent bonds;
In others, it plays the role of an active acceptor and is used in practical devices.

However, the above-mentioned valence-electron-controlled acceptor atom is unlikely to be an effective acceptor in a semiconductor such as ZnSe having a higher degree of ionic bondability than that of a covalent bond, and is therefore an acceptor element which can be used as a practical device until now. Not. The reason for this is that if a valence-controlled acceptor atom considering only covalent bond properties is added to ZnSe or the like having a strong ionic bond property, the ionic bond balance will be lost in the vicinity of impurity atoms that have replaced atoms of the host crystal. , The atomic position is displaced from the normal position,
Microscopic defects are necessarily formed.

[0005] The present invention relates to the instability, low activation rate, and acceptability of conventional acceptor impurities (such as lithium, nitrogen, oxygen, etc.) in wide bandgap II-VI compound semiconductors such as ZnSe. The purpose of the present invention is to form a crystal layer exhibiting p-type conduction with good reproducibility, and to reduce p-type conductivity in a visible short wavelength region such as blue. -To contribute to the realization of an n-junction semiconductor light emitting device.

[0006]

To achieve the above object, the present invention provides a high energy band gap (Eg ≧
The present invention is characterized by a p-type II-VI group compound semiconductor having a resistivity of 2.3 eV) and containing fluorine (F) as an acceptor impurity. In other words, the present invention achieves p-type conduction by adding an “ionic control acceptor” element different from the conventional valence control acceptor element (lithium, nitrogen, etc.). However, it is not easy to find such an acceptor element among wide band gap (Eg ≧ 2.3 eV) II-VI compound semiconductors such as ZnSe, and no suitable element has yet been found. The present inventor has conducted various studies to solve this problem, and as a result, has completed the present invention.

[0007] Fluorine (F), a new acceptor element, has a much higher electron affinity than the constituent elements of the host crystal and is locally negatively charged, thereby effectively creating holes in the valence band. Supply. Further, the fluorine acceptor of the present invention is characterized in that since the atomic radius is small, the strain induced in a crystal lattice of a II-VI group compound semiconductor such as ZnSe as a base is small, and a high activation rate as an acceptor is exhibited. In addition, it has the effect of reducing composite defects due to addition.

[0008]

[Function] In the conventional acceptor addition, p-type conduction II
Although the carrier concentration of the -VI group compound semiconductor was limited to the order of 10 ¹⁶ cm ^-3 , the carrier concentration of 10 ¹⁷ c
It became possible to obtain m ⁻³ p-type crystal layers with good reproducibility. This makes visible short wavelength light emitting devices (LD, LED)
The pn junction which is the basic structure of II-V
It can be mass-produced using a group I compound semiconductor.

[0009]

Next, an embodiment of the present invention will be described. It should be noted that the embodiments are merely examples, and it is needless to say that various changes or improvements can be made without departing from the spirit of the present invention.

(Embodiment 1) In the present invention, ZnSe
The case of fluorine ion implantation into the substrate will be described. MOVPE
Method (metalorganic vapor phase epitaxy) using semi-insulating GaAs (10
0) Non-doped ZnSe film (thickness of about 3
μm) at an acceleration energy of 200 keV and a dose of 5 × 10 ¹² cm ⁻² for fluorine ions.
Thermal annealing was performed at 0 ° C. for 5 minutes.

From the results of the photoluminescence measurement and the hole measurement, it was found that the heat-treated ZnSe film became p-type conductive. Also, (a) the depth of the energy level of fluorine as an acceptor is 85 to 90 meV, which is shallower by about 25 meV than the value of a conventional nitrogen acceptor or the like. (B) The concentration of fluorine atoms introduced by ion implantation of 1 × A hole concentration of 1 to 5 × 10 ¹⁵ cm ⁻³ is obtained with respect to 10 ¹⁷ cm ⁻³ (according to mass microanalysis), and the hole activation rate is at least one order of magnitude higher than the conventional acceptor Showed excellent acceptor properties.

In the next embodiment, ZnS _x Se _1-x (0 <
An example in the case of growth doping in which fluorine is added as an acceptor during the growth of a crystal film of x <1) and Zn _x Cd ₁ -xS (0 <x <1) will be described. (Embodiment 2) In this embodiment, ZnS _0.07 S is used as a II-VI group compound semiconductor.
The case where fluorine is added by MOVPE using e _0.93 , (100) GaAs as a substrate crystal, and Ar as a raw material dilution and growth atmosphere gas will be described.

FIG. 1 shows the MOVP used in this embodiment.
The outline of an E apparatus (organic metal vapor phase epitaxy apparatus) is shown. In the figure, 1 is a reactor, 2 is a substrate, 3 is a high frequency coil, 4 is a substrate holder, 5 is an oxygen cylinder, 7 is a hydrogen sulfide cylinder,
6, 10, 11, 13, 14, 16 are gas flow controllers, 8 is an exhaust boat, 9 is diethyl zinc, 12 is a hydrogen selenide cylinder, and 15 is an inert gas introduction line.

In this embodiment, ZnS _0.07 Se _0.93
Diethylzinc (C ₂ H) as a raw material for growing
₅ ) ₂ Zn: hereinafter abbreviated as DEZ｝, hydrogen sulfide (H ₂
S), and hydrogen selenide (H ₂ Se). These raw materials are stored in the bubbler container 9 and the cylinders 7 and 12 in FIG. 1, respectively. The flow rate of the Ar gas supplied from the introduction line 15 is controlled by the flow rate controller 13 and sent to the DEZ bubbler 9 to carry out the DEZ vapor from the bubbler. The carried-out DEZ vapor is diluted with Ar gas sent from the flow controller 14 and introduced into the reactor 1. The hydrogen sulfide and hydrogen selenide supplied from the cylinders 7 and 12 are controlled by the flow controllers 16 and 11,
, And is introduced into the reaction furnace 1. Fluorine, which is a dopant, is supplied at a controlled flow rate by a flow controller 6 using fluorine gas stored in a cylinder 5 as a raw material. These raw materials were placed on a substrate holder 4 heated by a high frequency coil 3 (10
0) Fluorine-doped ZnS mixed just above the GaAs substrate 2
_0.07 Se _0.93 crystals are deposited on the substrate.

Using the growth apparatus of FIG. 1, p-type conduction ZnS _0.07 Se by addition of fluorine within the range of the following growth conditions:
Growth of _0.93 film has become possible on a 5 inch GaAs substrate. Growth temperature 230 ℃ ～ 550 ℃ Reactor pressure 1T
orr to 760 Torr Growth rate 5 μm / h or less Fluorine flow rate 1 to 10 cc / min

The obtained fluorine-doped p-type conductive ZnS _x Se
The carrier concentration of _1-x (x = 0 to 1) is 2 × 10 ¹⁶ cm ⁻³
~ 1 × 10 ¹⁷ cm ^-3 , mobility is 50-20 cm ² / V ·
s. In this embodiment, fluorine gas is used as the fluorine supply material, but other fluorine supply sources (PF ₃ , CF
Similar effects were confirmed by using ₄ ). It is obvious that fluorine can be added in a similar manner in the hydrogen-based MOVPE method.

(Embodiment 3) In this embodiment, II-
A case where Zn _0.4 Cd _0.6 S is selected as a VI group compound semiconductor, (100) GaAs is selected as a substrate crystal, and fluorine is added by MBE (molecular beam epitaxy) will be described.

FIG. 2 shows a schematic diagram of a molecular beam epitaxy apparatus. In the figure, 17 is an MBE apparatus, 18 is a substrate holder, 19 is a GaAs substrate, 20 is a ZnSe epitaxial film, 21 is a Knudsen cell for Zn, 22 is a Knudsen cell for Cd, and 23 is a Knudsen cell for S , 24 indicate Knudsen cells for ZnF ₂ .

In this embodiment, (Zn, Cd) S
Are grown in Knudsen cells 21, 22, and 23 (hereinafter referred to as K-cells), respectively, and the molecules are heated by heating the K-cells during growth. Supplied as a line. Fluorine, which is a p-type dopant, is similarly supplied from the K-cell 24 using ZnF ₂ as a raw material. Each molecular beam supplied from the K-cell is a GaAs substrate (1 in the figure) heated by a heater.
9) A fluorine-added Zn _0.4 Cd _0.6 S film 20 is formed thereon.

Using the above-described growth apparatus, a fluorine-added Zn _0.4 Cd _0.6 S film can be grown under the following growth conditions. Substrate temperature 200-450 ° C
Growth rate 3 μm / h or less Molecular beam intensity ratio 0.2 ≦
(Zn + Cd) /S≦3,0.5≦Zn/Cd≦4K−
Cell temperature ZnF ₂ cell; 300-950 ° C

The obtained fluorine-doped p-type conductive Zn _x Cd _{1 -x}
The carrier concentration of S (x = 0.4 to 0.7) is 2 × 10
^The control was possible within the range of ^{16 to} 5 × 10 ¹⁷ cm ⁻³ , and the mobility was 20 to 50 cm ² / V · s. Further, another fluorine source (such as CdF ₂ ) may be used, or a gas source MBE may be used.
Gaseous fluorine source (F ₂ , NF ₃ , PF ₃ ,
It has been confirmed that the same effect can be obtained by using CF ₄ or the like.

Next, using the present invention, the p
An -n junction light emitting diode was manufactured. FIG. 3 shows the structure of the light emitting diode. In the figure, 25 is an Au electrode, 26
Is p-ZnS _0.06 Se _0.94 and 27 is n-ZnS _0.06 Se
_0.94 and 28 indicate n-GaAs substrates.

In manufacturing, n-type GaAs 2
8 (carrier concentration: 10 ¹⁸ cm ⁻³ ) and an iodine-doped n-type ZnS _0.06 Se _0.94 film 27 (carrier concentration: 5 × 10
¹⁸ cm ^-3 and a film thickness of 1.5 μm).
P-type conductive ZnS _0.06 Se using NF ₃ as a dopant material
_0.94 film 26 (carrier concentration 5 × 10 ¹⁶ cm ⁻³ , film thickness 1.
5 μm) to produce a diode.

As shown in FIG. 4, this diode emitted strong blue light at room temperature with a forward bias of about 3.2 V, in which light emission at a deep level was suppressed. In FIG. 4, the horizontal axis represents wavelength, and the vertical axis represents emission intensity.

[0025]

According to the present invention, a low resistance p-type II-VI
Since a group III compound semiconductor thin film can be obtained with good reproducibility,
It becomes possible to mass-produce the junction type blue light emitting element. The present invention ternary or more solid solution system, the use of relative _{Zn x Cd 1-x S y} Se 1-y, but also be effective in the development of p-n heterojunction for the blue semiconductor laser diode It is.

[Brief description of the drawings]

FIG. 1 shows a schematic diagram of a MOVPE apparatus.

FIG. 2 shows a schematic diagram of an MBE device.

FIG. 3 shows the structure of a ZnS _0.06 Se _0.94 pn junction light emitting diode formed using the present invention.

FIG. 4 shows an emission spectrum at room temperature of a pn junction light emitting diode formed using the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Reaction furnace 2 Substrate 3 High frequency coil 4 Substrate holder 5 Oxygen cylinder 7 Hydrogen sulfide cylinder 6,10,11,13,14,16 Gas flow controller 8 Exhaust boat 9 Diethyl zinc 12 Hydrogen selenide cylinder 15 Inert gas introduction line 17 MBE apparatus 18 Substrate holder 19 GaAs substrate 20 ZnS epitaxial film 21 Knudsen cell for Zn 22 Knudsen cell for Cd 23 Knudsen cell for S 24 ZnF ₂
Knudsen cell 25 Au electrode 26 p-ZnS _0.06 Se _0.94 27 n-ZnS _0.06 Se _0.94 28 n-Ga
As substrate

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takato Ando 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Sakae Mabufo 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo No. Nippon Telegraph and Telephone Corporation (72) Inventor Akinori Katsui 1-6-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-2-56975 (JP, A) JP-A Heisei 2-87685 (JP, A) JP-A-2-114677 (JP, A) JP-A-2-122565 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 33/00 H01L 21/203

Claims (2)

(57) [Claims] 1. A high energy band gap (Eg ≧
2.3 eV) and containing fluorine (F) as an acceptor impurity. 2. A high energy band gap (Eg ≧
Has a 2.3 eV), and ZnSe or ZnS or CdS or ternary mixed crystal of those containing fluorine (F) as an acceptor _{impurity, Zn x Cd 1-X S} , Z n Se y
A p-type II-VI compound semiconductor, wherein S _1-y (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).