Materials Science in Electronics devices

- Semiconductor devices -

2015 Yutaka Oyama

oyama@material.tohoku.ac.jp

http://www.material.tohoku.ac.jp/~denko/lab.html

Contents

・ Material issue of semiconductor devices and fabrication process

• Schematics of thin film growth (Molecular Layer Epitaxy, etc.)

・ Ultra fast and high frequency semiconductor electronic and photonic devices -1

• Ultra fast and high frequency semiconductor electronic and photonic devices -2

・ Crystal growth and semiconductor device epitaxy

・ Device grade evaluation of semiconductor crystals

UV

Blue

Green

Yellow

Orange

red

wavelength

color

Energy[eV] wavelength frequency

infrared

UV

X-ray

photonConductionband

Valenceband

Conductionband

Valenceband

photon

Direct transition

Electron/hole and photon interaction

High emission efficiency

Indirect transition

Electron/hole and lattice vibration (phonon) interaction

Low emission efficiency

lattice vibration (phonon)

発光色

発光領域となるp型半導体の、伝導帯と価電子帯のエネルギー差（バンドギャップ）が大きいほど、電子が伝導帯から価電子帯へ落ちるときに発せられる光のエネルギーは大きなものとなる。また、光の色は波長によって変化する。また波長は光のエネルギーが大きいほど短いものとなる。そのため、光の色は半導体のバンドギャップの大きさによって左右されることになる。バンドギャップは材料によってほぼ決まるので、放出される光の色は材料によって決まるといえる。下の表に、材料と光の色との関係を示した。

色 材料 material ピーク波長 wavelength接合構造

青

InGaN 450 量子井戸

ZnCdSe 489 ダブルへテロ

緑

ZnTeSe 512 ダブルへテロ

GaP 555 ホモ接合

黄

AGaInP 570 ダブルへテロ

InGaN 590 量子井戸

赤

AlGaAs 660 ダブルへテロ

GaP(Zn-0) 700 ホモ接合

赤外

GaAs(Si) 980 ホモ接合

InGaAsP 1300 量子井戸

0.92

6.895.87 6.48

0.18

1.35

0

0.8

1.6

2.4

5.6 6.0 6.45.2

0.5

1.0

2.0

5.0

Lattice constant [Å]

Bandgap

[eV

]w

avele

ngth

[μm

]

GaP

GaAs

InP GaSb

InSb

0.92

6.895.87 6.48

0.18

1.35

0

0.8

1.6

2.4

5.6 6.0 6.45.2

0.5

1.0

2.0

5.0

Lattice constant [Å]

Bandgap

[eV

]w

avele

ngth

[μm

]

GaP

GaAs

InP GaSb

InSb

半導体結晶の格子定数と禁制帯幅Lattice constants & band gap energies

c

hE

electron charge q is 1.602x10-19 [C],

Plank constant h is 6.626×10-34[J・s],

light velocity in vacuum c is

3×108[m/s].

主な光デバイス半導体材料の格子定数とEg（＝色）

Lattice constant [A]

Band gap energy[eV]

Lattice fitting is one of the most important factor for high quality crystal growth

Lattice mismatch will introduce serious crystalline defects into device structure.

Trend of LED luminescent efficiency

~mm-10mm

~100mm

（THｚ wave）

GaP

LiNbO

DAST

GaSe

ZnGeP

PbTe

PbSnTe

HgCdTe

医療応用生体分子ｽﾍﾟｸﾄﾛｽｺﾋﾟｰ

励起・治療

ﾘﾓｰﾄｾﾝｼﾝｸﾞ（Nox、CO2・・）非石英系ﾌｧｲﾊﾞｰ通信（超低損失）

IR

(infrared)

Visible light

UV light

発光デバイス発光ダイオード（＝PNダイオード）

Light emitting diode (LED) = PN diode structure

Minority carrier diffusion length of electron in p-type region is longer than that of hole in n-region,Thus light emission will enhanced at the p-side interface region of pnjunction.

発光ダイオードの光損失Reduction of emitted light intensity inside the semiconductors

Light absorption within semi.

Fresnel reflection at the semi. Air interface due to refractive index difference

Total reflection phenomenon at the semi/air interface

同種接合ホモ接合

異種接合ヘテロ接合

量子井戸構造

発光効率向上のための接合構造 Junction structures for improved luminescence

efficiency

電流狭さく構造光閉じ込め効果（屈折率大＜屈折率小）

Confinement of

Current & light

Homo junction

Hetero junction

発光ダイオード（LED)の高効率化

Double hetero junction structure

Enhancement of light emission efficiency of LED

Carrier confinement by potential barrierLight confinement by high refractive index of active region

No absorption of light within cladding layer of AlGaAs

発光デバイス半導体レーザ

Spontaneous emission (natural) Stimulated emission

LASER (Light Amplification by Stimulated Emission of Radiation

ConductionBand

Valenceband

自然放出と誘導放出

Spontaneous emission & Stimulated emission

Phase of light is randomized not single frequency (wavelength)

Phase of light is single (coherent) Single frequency light

Spontaneous emission

Stimulated emission

光学遷移確率

Optical transition probability

Spontaneous emission

Stimulated emission

Inter band absorption

半導体レーザの共振器構造

Cavity of semiconductor laser

Total reflectionMirror

Partial reflectionMirror

Lasing media(lasing material)

Excitation light

半導体レーザの構造＝LEDとほとんど同じ

LD structure is almost the same as that of LED

Cladding layer

Cladding layer

Active layer

Ex.cleaving

光（増幅）利得 ｇ

電子の反転分布（負の温度）

Condition for light amplification

Normal semi. condition Abnormal (inversion distribution of electrons)

Inversion distribution=Negative temperature FD distribution

半導体レーザの光スペクトラム

Typical emission spectra of LD

半導体レーザのﾋﾞｰﾑプロファイル

Light beam profile from LD

レーザﾋﾞｰﾑの近視野像と遠視野像Near field and far field beam profiles of LD

電流ー光室力特性（しきい値電流）

Threshold current for lasing

低次元構造（量子井戸構造など）を用いたLD

Low dimensional structures for LDValence band is degenerated(light hole and heavy hole)Effective mass difference

ストライプ構造のレーザ

Stripe laser diode (edge emitting diode)

半導体レーザの構造例 (edge emitting laser)

Some tricky structure of LDApplication of amphoteric impurity site occupation difference between (111) sidewall and (100) surface

面発光レーザ vertical cavity laser

分布帰還形レーザ（Distributed FeedBack laser) :DFB laser波長選択性 波長可変半導体レーザ (tunable laser)

白色発光ダイオード

White light LED

長い

Operation principle of white light LED

Yellow light is emitted from the absorbed blue

or UV from LED, then the white light is

generated by the mixture of yellow and blue.

Very interesting history of LASER invention

1917 Albert Einstein: Zur Quantentheorie der Strahlung（放射の量子論について）1928 Rudolf W. Ladenburg: stimulated emission & negative absorption1939 Valentin A. Fabrikant: prediction of light amplification1947 Wilis Ram R. C. Retherford: first appearance of stimulated emission (hydrogen emission)1950 Alfred Castlel: proposal of light pumping method1953 Charles Towns, James P. Gordon(Student), Herbert J. Zeiger: Microwave amplification by solid (MASER)1953 Von Neuman: idea of semi. Laser by private letters to friends1957 Yasushi Watanabe, Jun-ichi Nishizawa (TOHOKU Univ.): JP patent of semi. LASER（特公昭35-13787）

1957 James P. Gordon: idea of open light cavity (exp. Notes) evidence for patent !

1959 April James P. Gordon: USP of LASER but canceled1960 Theodore Harold Maiman: realization of LASER (AlO3:Cr LASER)1962 Robert N. Hall: GaAs IR LASER at 77K1970 Iwao Hayashi, Morton Panish: RT LD using double hetero junction1987 James P. Gordon was formally assigned as LASER inventor by US court