JP3904709B2 - Nitride-based semiconductor light-emitting device and method for manufacturing the same - Google Patents

Description

【００６６】
次に、本発明者は、成長温度を７６０℃に固定し、原料ガスとキャリヤガスの流量の総和を１分あたり３０リットルにし、Ｖ族元素とIII 族元素のモル流量比依存性を調べた。その結果、表２の様にＶ族元素とIII 族元素のモル流量比が１０００以上１５０００以下では十分な強度のＰＬ発光が見られた。
Ｖ族元素とIII 族元素のモル流量比が１０００を下回ると、十分に反応しないため、ＰＬ発光強度が上がらない。
Ｖ族元素とIII 族元素のモル流量比が１５０００を上回ると、本来III 族元素が反応するべき結晶格子にもＶ族元素が割り込んで反応してしまい、III 族元素が十分に反応できないため、ＰＬ発光強度が極端に低減した。
【００６７】
【表２】

【００６８】
さらに、成長温度を７６０℃に固定し、Ｖ族元素とIII 族元素の流量比を８４００にし、すべての原料ガスとキャリヤガスの１分間あたりの総流量に対する依存性を調べたところ、表３の様に一分間あたりの総流量が１０リットル以上、５０リットル以下では十分な強度のＰＬ発光が見られた。一分間あたりの総流量が１０リットルを下回ると、十分に反応しないため、ＰＬ発光強度が上がらない。一分間あたりの総流量が５０リットルを上回ると、流速が早くなり、十分な反応時間がとれないため、ＰＬ発光強度が極端に低減した。
【００６９】
【表３】

【００７０】
本実施形態では、ＩｎＧａＮ多重量子井戸活性層５０５およびノンドープＧａＮ隣接層５０６ともに意図的にはドーピングを施していない。本発明者の実験によれば、上記のように成長した場合、ＧａＮ層の方がＩｎＧａＮ層よりも高抵抗であることがわかっている。また、上記のように成長したものの断面をＴＥＭ（透過電子顕微鏡）で観察したところ、 ＩｎＧａＮ多重量子井戸活性層５０５に穴状領域（ピット）が存在し、このピットがノンドープＧａＮ隣接層５０６によって埋め込まれ、平坦化されていることがわかった。従って前記の実施形態の半導体発光素子によれば、以下に述べる原理により自励発振が生じる。
【００７１】
すなわち、活性層に穴状領域が存在することにより、活性層内を流れる電流に分布ができ、低電流密度領域が可飽和吸収領域となるので、自励発振が生じる。このことについて以下に詳述する。
【００７２】
図１６は、本実施形態の発光素子における注入電流の流れを示す断面模式図である。同図においては、分かり易くするために、図１６に示した発光素子の構造を簡略化した構造を例示して説明する。図１６に示したように、ノンドープＧａＮ層５５３とノンドープＩｎＧａＮ層５５４のヘテロ接合があり、しかもノンドープＩｎＧａＮ層５５４側の界面には穴（ピット）Ｐがある。両者にはそれぞれｐ型コンタクト層５５２、ｎ型コンタクト層５５５を介してｐ側電極５５１、ｎ側電極５５６が接続されている。
【００７３】
いま、両電極に順方向に電圧をかけたとすると、ノンドープＧａＮ層５５３の方がノンドープＩｎＧａＮ層５５４に比べてバンドギャップが大きいために、電流は図１６中の矢印で示すように流れ、ＩｎＧａＮ層５５４のうちの穴状領域の下の部分の電流密度は他の領域の電流密度に比べて、疎になる。
【００７４】
本発明者は、この現象を実証するために二次元のシミュレーションを実行し、電流の分布を調べた。図１７にシミュレーションで用いた層構造を示す。層構造はレーザ構造を模したものであり、５×１０¹⁸ｃｍ^-3にドープされた厚さ０．１μｍのｎ型ＧａＮコンタクト層５６１、５×１０¹⁷ｃｍ^-3にドープされた厚さ０．３μｍのｎ型Ａｌ_0.15Ｇａ_0.85Ｎクラッド層５６２、厚さ０．１μｍのノンドープＧａＮ隣接層５６３、厚さ０．１μｍのノンドープＩｎ_0.08Ｇａ_0.92Ｎ活性層５６４、厚さ０．１μｍのノンドープＧａＮ隣接層５６５、５×１０¹⁷ｃｍ^-3にドープされた厚さ０．３μｍのｐ型Ａｌ_0.15Ｇａ_0.85Ｎクラッド層５６６、５×１０¹⁸ｃｍ^-3にドープされた厚さ０．１μｍのｐ型ＧａＮコンタクト層５６７からなる。ノンドープＩｎ_0.08Ｇａ_0.92Ｎ活性層５６４のノンドープＧａＮ隣接層５６３に接する界面には幅０．１μｍ、深さ０．０５μｍの穴状領域（ピット）Ｐが１μｍの間隔を置いて並んでいる。実際のピットの形状はこのような矩形では必ずしもないが、計算の簡便化のためにこのような形状でシミュレーションを行った。形状の違いがシミュレーション結果に本質的な影響を及ぼさないことは言うまでもない。
【００７５】
このような構造に４Ｖの電圧を印加した時の穴状領域（ピット）の直下での電流密度の分布を図１８に示す。ピットの部分で電流密度が３０％以上も低減している。このように電流の疎密が穴状領域の存在によってもたらされることが明らかとなった。そして、このような電流分布が生じることになり、レーザ発振が生じる際には、まず、電流が密な部分で発振が始まり、電流が疎の部分が可飽和吸収体となることになる。尚、隣接層がノンドープでなく、５×１０¹⁷ｃｍ^-3にドープされている場合についても同様の結果であった。このように、穴状領域が存在することで、電流の疎密が発生することになる。そして、電流が疎の部分は可飽和吸収体となり、自励発振が実現できる。
【００７８】
次に、本発明の第６の実施の形態について説明する。図１９は本発明の第６の実施形態に係わる窒化物系半導体発光素子の概略構成を説明するためのものである。同図において、７００はサファイア基板、７０１はバッファー層、７０２はｎ型ＧａＮコンタクト層（Ｓｉドープ、３〜５×１０¹⁸ｃｍ^-3、４μｍ）、７０３はｎ型ＡｌＧａＮクラッド層（Ｓｉドープ、５×１０¹⁷ｃｍ^-3、０. ３μｍ）、７０４はｎ型Ｉｎ_0.1 Ｇａ_0.9 Ｎ／Ｉｎ_0.02Ｇａ_0.98Ｎ多重量子井戸隣接層（Ｓｉドープ、５×１０¹⁷ｃｍ^-3、井戸幅２ｎｍ、障壁幅４ｎｍ、２０層）、７０５はＩｎ_0.2 Ｇａ_0.8 Ｎ／Ｉｎ_0.05Ｇａ_0.95Ｎ多重量子井戸活性層（ノンドープ、井戸幅２ｎｍ、障壁幅４ｎｍ、１０層）、７０６はｐ型ＧａＮ隣接層（Ｍｇドープ、５×１０¹⁷ｃｍ^-3、０．１μｍ）、７０７はｐ型ＡｌＧａＮクラッド層（Ｍｇドープ、５×１０¹⁷ｃｍ^-3、０．３μｍ）、７０８はｐ型ＧａＮコンタクト層（Ｍｇドープ、５×１０¹⁸ｃｍ^-3、０．５μｍ）、７０９はＳｉＯ₂ 膜、７１０はｐ側電極、７１１はｎ側電極である。
【００７９】
ｎ型Ｉｎ_0.1 Ｇａ_0.9 Ｎ／Ｉｎ_0.02Ｇａ_0.98Ｎ多重量子井戸隣接層７０４は次のように成長させる。成長温度は７６０℃で、Ｉｎ_0.1 Ｇａ_0.9 Ｎ井戸層の成長にはＴＭＩ、ＴＭＧ、アンモニア、ＳｉＨ₄ を用い、厚さが２ｎｍの井戸層を成長する。次に、１秒間、アンモニアだけを供給した状態で待機したのち、ＴＭＩ、ＴＭＧ、アンモニア、ＳｉＨ₄ を用いて厚さが４ｎｍのＩｎ_0.02Ｇａ_0.98Ｎ障壁層を成長する。つぎに再度１秒間の待機時間をおいて井戸層を同様に成長する。このようなプロセスを合計２０回繰り返すことでｎ型Ｉｎ_0.1 Ｇａ_0.9 Ｎ／Ｉｎ_0.02Ｇａ_0.98Ｎ多重量子井戸隣接層７０４が形成できる。
【００８０】
また、 Ｉｎ_0.2 Ｇａ_0.8 Ｎ／Ｉｎ_0.05Ｇａ_0.95Ｎ多重量子井戸活性層７０５の成長方法は次の通りである。７６０℃の成長温度で、Ｉｎ_0.2 Ｇａ_0.8 Ｎを２ｎｍ成長し、１秒間の待機時間を設てＩｎ_0.05Ｇａ_0.95Ｎを成長する。このサイクルを合計１０回繰り返す。
【００８１】
このような成長方法によってｎ型Ｉｎ_0.1 Ｇａ_0.9 Ｎ／Ｉｎ_0.02Ｇａ_0.98Ｎ多重量子井戸隣接層７０４とＩｎ_0.2 Ｇａ_0.8 Ｎ／Ｉｎ_0.05Ｇａ_0.95Ｎ多重量子井戸活性層７０５共に、島状領域を有し、かつ、ピットを有する構造を形成することが可能となる。
【００８２】
以上、具体例を参照しつつ、本発明の実施の形態について説明した。しかし、本発明はこれらの具体例に限定されるものではない。例えば、前述した第１から第６の実施形態では活性層はノンドープ層であるが、ｎ型あるいはｐ型にドープされていても良い。またこれに隣接する層はドーピングされていなくても、あるいはｎ型やｐ型にドーピングされていても良い。その他、本発明はその要旨を逸脱しない範囲で種々変形して実施できる。
【００８３】
【発明の効果】
以上詳述したように本発明の窒化物系半導体レーザによれば、複雑な構造を用いずに、自励発振を生じる窒化物系半導体発光素子が高い確率で得られる。これによって、低ノイズの特性をもった光ディスク記録の読み出し用半導体レーザとして実用可能な性能を満たした半導体レーザを安価に容易に作成でき、その有用性は絶大である。さらに、同じ構造の窒化物系半導体レーザにより記録媒体からの読み出しおよび書き込みが可能になり読み出し書き込み兼用へッドの構造を飛躍的に単純化できた。
一方、本発明の窒化物系半導体発光ダイオードによれば、発光効率の高い窒化物系発光ダイオードが得られた。
【図面の簡単な説明】
【図１】 本発明の窒化物系半導体発光素子の第１の実施形態を示す断面図である。
【図２】 図１に示す多重量子井戸隣接層１０４の面内発光分布を表す模式図である。
【図３】 図１に示す多重量子井戸隣接層１０４におけるＩｎ組成比とドナー濃度の関係を示すグラフである。
【図４】 図１に示す多重量子井戸隣接層１０４におけるバンド構造を示す模式図である。
【図５】 図１に示す窒化物系半導体発光素子の光出力に対する自励発振生起割合を示すグラフである。
【図６】 半導体レーザを光ディスクの読み出しに応用した状態を説明する模式図である。
【図７】 本発明の窒化物系半導体発光素子の第２の実施形態を示す断面図である。
【図８】 図７に示す活性層２０５を透過型電子顕微鏡により観察した結果を表す模式図である。
【図９】 図７に示す窒化物系半導体発光素子の製造条件を示すグラフである。
【図１０】 本発明の窒化物系半導体発光素子の第３の実施形態を示す断面図である。
【図１１】 図１０に示す窒化物系半導体発光素子に用いる基板の構造を示す概略図で、（ａ）は平面図、（ｂ）は側面図である。
【図１２】 図１０に示す活性層３０５の透過型電子顕微鏡による観察の結果を表す模式図である。
【図１３】 図１０に示す活性層３０５における島状領域の平均径と半導体発光素子の外部量子効率の関係を示すグラフである。
【図１４】 本発明の窒化物系半導体発光素子の第４の実施形態を示す断面図である。
【図１５】 本発明の窒化物系半導体発光素子の第５の実施形態を示す断面図である。
【図１６】 隣接層が活性層よりもバンドギャップが大きいの場合の電流経路を示す概略図である。
【図１７】 ２次元のシュミレーションで用いた層構造を示す概略図である。
【図１８】 図１７に示した素子に対する２次元のシュミレーションにおいて４Ｖの電圧を印加した時の穴状領域の直下での電流密度の分布図である。
【図１９】 本発明の窒化物系半導体発光素子の第６の実施形態を示す断面図である。
【符号の説明】
１００ サファイヤ基板，
１０１ ｎ型ＧａＮバッファー層
１０２ ｎ型ＧａＮコンタクト層
１０３ ｎ型ＡｌＧａＮクラッド層
１０４ ｎ型Ｉｎ_0.1 Ｇａ_0.9 Ｎ／ＧａＮ多重量子井戸隣接層
１０５ Ｉｎ_0.3 Ｇａ_0.7 Ｎ／ＧａＮ多重量子井戸活性層
１０６ ｐ型ＧａＮ隣接層
１０７ ｐ型ＡｌＧａＮクラッド層
１０８ ｐ型ＧａＮコンタクト層
１０９ ｎ型ＧａＮ通電障壁層
１１０ ｐ側電極
１１１ ｎ側電極
１５０ レーザ光
１５２ レンズ
１５４Ａ 本発明による窒化物系半導体レーザ・ビーム
１５４Ｂ 従来のＤＶＤシステムのレーザ・ビーム
１５４Ｃ コンパクト・ディスクシステムのレーザ・ビーム
１６０ 光ディスク
１６２ トラック
１６４ ピット
２００ ｐ型ＳｉＣ基板
２０１ ｐ型ＡｌＮバッフア層
２０２ ｐ型ＧａＮ層
２０３ ｐ型Ａｌ_0.3 Ｇａ_0.7 Ｎクラッド層
２０４ Ａｌ_0.1 Ｇａ_0.9 Ｎ隣接層
２０５ Ｉｎ_0.1 Ｇａ_0.9 Ｎ／Ａｌ_0.1 Ｇａ_0.9 Ｎ多重量子井戸活性層
２０６ Ａｌ_0.1 Ｇａ_0.9 Ｎ隣接層
２０７ ｎ型Ａｌ_0.3 Ｇａ_0.7 Ｎクラッド層
２０８ ｐ型ＧａＮ電流狭窄層
２０９ ｎ型ＧａＮコンタクト層
２１０ ｎ側電極
２１１ ｐ側電極
３００ サファイヤ基板
３０１ ＧａＮバッファー層
３０２ ｐ型ＧａＮコンタクト層
３０３ ｐ型Ａｌ_0.2 Ｇａ_0.8 Ｎクラッド層
３０４ ｐ型ＧａＮ隣接層
３０５ Ｉｎ_0.3 Ｇａ_0.7 Ｎ／ＧａＮ多重量子井戸活性層
３０６ ｎ型ＧａＮ隣接層
３０７ ｎ型Ａｌ_0.2 Ｇａ_0.8 Ｎクラッド層
３０８ ｐ型ＧａＮ通電障壁層
３０９ ｎ型ＧａＮコンタクト層
３１０ ｎ側電極
３１１ ｐ側電極
４００ サファイヤ基板
４０１ ＧａＮバッファ層
４０２ ｎ型ＧａＮコンタクト層
４０３ ｎ型 ＧａＮ層
４０４ Ｉｎ_0.3 Ｇａ_0.7 Ｎ／ＧａＮ ３ＭＱＷ活性層
４０５ ｐ型 ＧａＮ層
４０６ ｐ型ＧａＮコンタクト層
４１０ ｐ側電極
４１１ ｎ側電極
４１２ ＩＴＯ透明電極
５００ サファイア基板
５０１ バッファ層
５０２ ｎ型ＧａＮコンタクト層
５０３ ｎ型ＡｌＧａＮクラッド層
５０４ ノンドープＧａＮ隣接層
５０５ ＩｎＧａＮＭＱＷ活性層
５０６ ノンドープＧａＮ隣接層
５０７ ｐ型ＡｌＧａＮクラッド層
５０８ ｐ型ＧａＮコンタクト層
５０９ ＳｉＯ₂ 膜
５１０ ｐ側電極
５１１ ｎ側電極
５５１ ｐ側電極
５５２ ｐ型コンタクト層
５５３ ノンドープＧａＮ層
５５４ ノンドープＩｎＧａＮ層
５５５ ｎ型コンタクト層
５５６ ｎ側電極
Ｐ ピット
５６１ ｎ型ＧａＮコンタクト層
５６２ ｎ型Ａｌ_0.15Ｇａ_0.85Ｎクラッド層
５６３ ノンドープＧａＮ隣接層
５６４ ノンドープＩｎ_0.08Ｇａ_0.92Ｎ活性層
５６５ ノンドープＧａＮ隣接層
５６６ ｐ型Ａｌ_0.15Ｇａ_0.85Ｎクラッド層
５６７ ｐ型ＧａＮコンタクト層
７００ サファイヤ基板
７０１ バッファー層
７０２ ｎ型ＧａＮコンタクト層
７０３ ｎ型ＡｌＧａＮクラッド層
７０４ ｎ型Ｉｎ_0.1 Ｇａ_0.9 Ｎ／Ｉｎ_0.02Ｇａ_0.98Ｎ多重量子井戸活性層
７０５ Ｉｎ_0.2 Ｇａ_0.8 Ｎ／Ｉｎ_0.05Ｇａ_0.95Ｎ多重量子井戸活性層
７０６ ｐ型ＧａＮ隣接層
７０７ ｐ型ＡｌＧａＮクラッド層
７０８ ｐ型ＧａＮコンタクト層
７０９ ＳｉＯ₂ 膜
７１０ ｐ側電極
７１１ ｎ側電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting device using a nitride compound semiconductor such as GaN, AlGaN, InGaN, and the manufacturing method thereof.
[0002]
[Prior art]
Regarding nitride compound semiconductors, hexagonal crystals grown on a substrate such as sapphire, SiC, and spinel are currently the best crystals. However, since the sapphire substrate and the spinel substrate have low conductivity, both the p-type and n-type electrodes are formed on the surface of the nitride semiconductor. In a high current injection such as a semiconductor laser, a so-called leak current that flows a large amount of current occurs on the surface, and the current that contributes to light emission is small. Furthermore, it is difficult to form a current confinement structure for preventing leakage current and increasing the current density necessary for operating the semiconductor laser at a low current. For this reason, conventionally, a semiconductor laser structure having a low operating current and no leakage current even at high current injection and having high reliability has not been obtained.
[0003]
In addition, a conventional semiconductor laser as a read-out optical head for optical disc recording has a problem of noise due to intensity change during oscillation. For example, a self-oscillation type structure is used as a countermeasure, but an ultra-thin active It is difficult to obtain self-excited oscillation in the layer structure. For this reason, a high-frequency superposition method or a method using two kinds of lasers is adopted, but the structure is complicated. In addition, a method of forming two types of lasers by changing the thickness of the active layer depending on the location has been reported, but this method has a problem that it is extremely difficult to control the thickness of the active layer. In general, a head for reading and writing uses two types of lasers having different outputs, but the structure of both is complicated.
[0004]
[Problems to be solved by the invention]
As described above, it has been difficult for a conventional nitride semiconductor laser to easily and inexpensively produce a semiconductor laser satisfying a practical performance as a read-side light head for optical disk recording.
[0005]
Accordingly, an object of the present invention is to provide a nitride-based semiconductor light-emitting device capable of performing self-excited oscillation with a simple structure, and a method for manufacturing the same, in consideration of the above circumstances.
[0006]
[Means for Solving the Problems]
  In the first invention of the present application, a mixed crystal layer composed of a ternary or more group III-V compound semiconductor having a hexagonal crystal structure including an active layer and an adjacent layer adjacent thereto is formed on a substrate. In the nitride semiconductor light emitting device, the adjacent layerHas a multiple quantum well structure containing InGaN, and the adjacent layerMake up this adjacent layerindiumDotted with islands with higher concentrations ofThe island regionThe nitride-based semiconductor light-emitting device is characterized in that the maximum diameter is 100 nm or less and the impurity concentration of the island-like region is lower than the impurity concentration of the peripheral portion.
[0007]
The second invention of the present application is the nitride according to the first invention, wherein the active layer is dotted with hole-like regions, and the hole-like regions are filled with a semiconductor forming the adjacent layer. This is a semiconductor light emitting device.
[0008]
  A third invention of the present application is the nitride-based semiconductor light-emitting element according to the first invention, wherein the adjacent layers are dotted with hole-like regions.The
[0009]
  No. of this application4In the present invention, the active layer has a multi-quantum well structure, and the active layer constitutes the active layer.indiumThe island-like regions having a higher concentration than that of the surrounding region are dotted, and the island-like regions have the same band gap as that of the material surrounding the region, or have a band gap that is small by a difference within 10 meV. A nitride-based semiconductor light-emitting device according to the first aspect of the invention.
[0010]
  No. of this application5In the invention, the impurity is at least one of Si, C, Ge, Sn, and Pb.4The nitride-based semiconductor light-emitting device described in the invention.
[0011]
No. of this application6According to the invention, λm = 2nd (m = 1, 2, 3, 4) where d is the distance between the island regions, n is the refractive index of the periphery thereof, and λ is the emission wavelength of the island regions. Said first having4The nitride-based semiconductor light-emitting device described in the invention.
[0012]
  No. of this application7In the invention of the present invention, the active layer is dotted with hole-like regions, the hole-like regions are embedded with a semiconductor forming the adjacent layer, and the adjacent layer is dotted with hole-like regions, The hole-shaped region is buried by a semiconductor forming a layer adjacent to the adjacent layer and not on the active layer side.4Thru6The nitride-based semiconductor light-emitting device described in the invention.
[0017]
  No. of this application9According to the present invention, a nitride layer is formed by laminating a mixed crystal layer composed of a ternary or more group III-V compound semiconductor having a hexagonal crystal structure, including an active layer and an adjacent multiple quantum well layer on the substrate. In the method for manufacturing a physical semiconductor light emitting device, the multiple quantum well adjacent layer has a multiple quantum well structure containing InGaN, and the source gas for growing the well layer and the source gas for growing the barrier layer are alternately used. The well layer and the barrier layer are alternately grown by supplying for a predetermined time, and a predetermined waiting time is provided between the growth of the well layer and the growth of the barrier layer. Nitride-based semiconductor having island-like regions having a maximum diameter of 100 nm or less, the concentration of indium constituting the quantum well adjacent layer being higher than that of the periphery and lower than the impurity concentration of the periphery. Light emission It is a manufacturing method of an element.
[0018]
  No. of this application10According to the present invention, the source gas for growing the well layer is trimethylindium, trimethylgallium and ammonia gas, and the source gas for growing the barrier layer is trimethylgallium and ammonia gas.9This is a method for manufacturing the nitride-based semiconductor light-emitting device described in the invention.
[0019]
  No. of this application13According to the present invention, a nitride layer is formed by laminating a mixed crystal layer composed of a ternary or more group III-V compound semiconductor having a hexagonal crystal structure, including an active layer and an adjacent multiple quantum well layer on the substrate. When manufacturing a physical semiconductor light emitting device by vapor phase growth using an organic metal, trimethylindium, trimethylgallium and ammonia gas are used as the raw material gas for the vapor phase growth, the growth temperature is set to 700 ° C. or higher and 850 ° C. or lower, In addition, the sum of all the raw material gases and the carrier gas flow rate is 10 to 50 liters per minute in standard conversion, and the molar flow rate ratio of the group V element to the group III element is 1000 to 15000,After the epitaxial growth of the active layer and further raising the temperature while flowing hydrogen, nitrogen, and ammonia, the hole-like regions formed in the active layer are filled with the semiconductor that forms the adjacent layer of the multiple quantum well.And a method for manufacturing a nitride-based semiconductor light-emitting device.
[0020]
In summary, according to the present invention, the self-excited oscillation is generated by making the active layer of the nitride semiconductor light emitting device or the adjacent layer adjacent to the active layer into a saturable absorption region.
[0021]
Therefore, according to the present invention, self-excited oscillation can be generated without using a complicated structure, and a read semiconductor laser for optical disk recording having low noise characteristics can be formed. Further, writing can be made with the same structure as that for reading, and the structure of the head for both writing and reading can be simplified.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a nitride-based semiconductor laser according to the first embodiment of the present invention. In the figure, 100 is a sapphire substrate, 101 is an n-type GaN buffer layer (Si dove, 3-5 × 10¹⁸cm^-3, 0.1 μm), and 102 is an n-type GaN contact layer (Si dove, 3-5 × 10¹⁸cm^-34 μm) and 103 are n-type AlGaN cladding layers (Si-doped, 5 × 10¹⁷cm^-3, 0.3 μm), 104 is n-type In_0.1 Ga_0.9 N / GaN multiple quantum well Adjacent layer (Si dove, 5 × 10¹⁷cm^-3Well width 2 nm, barrier width 4 nm, number of pairs 3), 105 is In_0.3 Ga_0.7 N / GaN multiple quantum well active layer (undoped, well width 2 nm, barrier width 4 nm, number of pairs 3), 106 is a p-type GaN adjacent layer (Mg doped, 5 × 10¹⁷cm^-3, 0.1 μm), 107 is a p-type AlGaN cladding layer (Mg-doped, 5 × 10¹⁷cm^-3, 0.3 μm), 108 is a p-type GaN contact layer (Mg-doped, 1-3 × 10¹⁸cm^-3, 0.5 μm), 109 is an n-type GaN conduction barrier layer (Si-doped, 1 × 10¹⁸cm^-30.3 μm), 110 is a p-side electrode, and 111 is an n-side electrode.
[0023]
The manufacturing method of the semiconductor laser shown in FIG. 1 is as follows. First, the n-type GaN buffer layer 101 to the n-type GaN layer 109 are grown on the sapphire substrate 100 by vapor phase growth (Metal Organic Chemical Deposition: MOCVD) using an organic metal. Thereafter, a mask is partially formed on the n-type GaN layer 109 by photolithography, and etching is performed until the p-type AlGaN cladding layer 107 is exposed. Next, the p-type GaN contact layer 108 is grown. Thereafter, in order to form the n-type GaN contact layer 102, the portion where the n-type GaN contact layer 102 is to be formed is covered with a mask and removed by etching. The nitride semiconductor laser having the structure of FIG. 1 can be manufactured by removing the mask and forming the n-side electrode 111 and the p-side electrode 110.
[0024]
Here, the n-type In_0.1 Ga_0.9 The N / GaN multiple quantum well adjacent layer 104 (Si-doped, well width 2 nm, barrier width 4 nm, number of pairs 3) is grown as follows. Growth temperature is 760 ° C, In_0.1 Ga_0.9 For the growth of the N layer, TMI (trimethylindium), TMG (trimethylgallium), ammonia gas, and silane are used, and growth is performed for 8 seconds under the condition that a growth rate of 1 μm / h is obtained by normal thick film growth. As a result, a well layer having a width of 2 nm is formed. Next, the substrate is grown for 18 seconds using TMG (trimethylgallium), ammonia gas, and silane with a waiting time of 1 second under the same growth rate conditions. As a result, a barrier layer having a width of 4 nm is formed. Thereafter, the same process was repeated three times to form three pairs of well layers and barrier layers.
[0025]
In the multi-quantum well adjacent layer 104 grown in this way, it has been found that a portion having a locally large In composition is formed in the in-plane direction of the layer.
FIG. 2 is a schematic diagram showing the in-plane distribution of the emission wavelength of the well layer of the multiple quantum well adjacent layer 104 by the cathode luminescence method. That is, in the figure, light emission having a wavelength longer than that of the surroundings was observed in the hatched region. In general, the wavelength of light emission obtained by the cathodoluminescence method varies depending on the composition of the target. Here, the greater the indium content, the longer the emission wavelength. That is, it was found that the multiple quantum well adjacent layer 104 has an island-like region having a high indium composition in the plane. As a result of examining the distribution state and the emission wavelength in detail, it is found that in each well layer of the multiple quantum well adjacent layer 104, a large number of island-like regions having a diameter of about 2 nm and an indium composition of about 30% are formed. It was. This island-like region has more In than the periphery, and has almost the same band gap as the band gap corresponding to the emission wavelength from the active layer 105. In addition, the multiple quantum well layer 104 is doped with silicon (Si) as described above. However, as shown in FIG. 3, the region having a high indium concentration is unlikely to contain silicon, and as a result, The carrier concentration in the portion where the indium concentration is high is low.
[0026]
FIG. 4 is a schematic diagram showing a state of a conduction band of an InGaN well layer and a GaN barrier layer pair in the multiple quantum well adjacent layer 104. That is, in the figure, the horizontal direction indicates the distance in the thickness direction of the adjacent layer 104, and the vertical direction indicates the energy level. As shown in the figure, the GaN barrier layer has a high concentration of donors and the energy band is greatly curved. Since the energy band is curved in this manner, the confinement of carriers in the InGaN well layer in this portion becomes weak for electrons having a small effective mass, and no light emission occurs. Further, when the active layer 105 emits light, absorption occurs in a portion with a large In composition in the adjacent layer 104, but the absorption occurs in a minute island-shaped region. Therefore, the adjacent layer 104 enters a saturable absorption state and a self-oscillation state. Such a self-excited oscillation state persisted even under high output conditions. If the impurity contained in the adjacent layer 104 is any one of n-type impurities such as silicon (Si), carbon (C), germanium (Ge), tin (Sn), and lead (Pb), There were no adverse effects such as an increase in threshold.
[0027]
The laser of this embodiment oscillated at room temperature at a threshold of 20 mA. The oscillation wavelength was 420 nm and the operating voltage was 3.8V. At 50 mW, the S / N was improved to 130 dB compared with 20 dB of the conventional semiconductor laser not using this structure. In addition, high output is difficult with a thick active layer self-pulsation type laser in which a saturable absorption layer is provided in the vicinity of a conventional active layer, but in this embodiment, output can be output in a stable transverse mode up to 200 mW. It was.
[0028]
Next, the present inventor manufactured a large number of nitride lasers of the present invention in which island-shaped absorption regions were formed by the above-described manufacturing method, and investigated the rate of occurrence of self-excited oscillation.
FIG. 5 is a graph showing the ratio of nitride-based semiconductor light-emitting elements in which self-oscillation occurs when the manufactured nitride-based semiconductor laser emits light while changing the light output. In the figure, the horizontal axis indicates the optical output, and the vertical axis indicates the ratio of nitride-based semiconductor light-emitting elements that have caused self-excited oscillation. Black circles in the figure represent the nitride-based semiconductor light-emitting device of the present invention. White circles in the figure are comparative examples, and show nitride-based semiconductor light-emitting elements in which layered absorption regions are formed instead of island-shaped absorption regions. This comparative example will be described in more detail. When viewed from the active layer, an In layer having a thickness of 10 nm is formed outside the guide layer._0.25Ga_0.75An N absorption layer was provided.
[0029]
From FIG. 4, in the comparative example in which the layered absorption region is provided, the rate of occurrence of self-oscillation is low and is not stable, whereas the nitride-based semiconductor of the present invention in which the island-shaped absorption region is formed It can be seen that the light-emitting element has a stable and high probability of obtaining a nitride-based semiconductor light-emitting element that generates self-excited oscillation from low output to high output.
[0030]
FIG. 6 is a schematic diagram for explaining a state in which the semiconductor laser according to the present invention is applied to data reading from an optical disk. That is, in the figure, a laser beam 150 is emitted from a semiconductor laser element (not shown), is focused by a lens 152, and enters the optical disc 160. On the surface of the optical disk 160, tracks 162 are provided on concentric circles, and pits 164 are formed along the tracks 162. The reflectance of the laser light focused by the lens 152 changes depending on the presence or absence of the pit 164, and is detected by a light receiving unit (not shown). Here, when a laser beam having a wavelength of 420 nm obtained from the nitride-based semiconductor laser according to the present invention is used, an extremely thin beam 154A can be obtained by being focused by a lens as shown in FIG. For comparison, the figure shows a conventional laser beam 154B of a DVD system (wavelength: λ = 650 nm, aperture ratio: NA = 0.6) and a compact disk system (wavelength: λ = 780 nm, aperture). Laser beam 154C with a ratio: NA = 0.45). As is clear from these comparisons, when the nitride-based semiconductor laser of the present invention is used, a very focused laser beam can be obtained, and the distance between the tracks 162 and the distance between the pits 164 in the optical disk 160. Can be reduced respectively. As a result, the recording capacity can be increased about three times as compared with the conventional DVD system.
[0031]
Furthermore, according to the nitride semiconductor laser of the present invention, reading and writing from an optical recording medium can be performed by the same nitride semiconductor laser. That is, since the semiconductor laser of the present invention easily generates self-excited oscillation, data reading can be stably performed with low noise, and further, a high output operation is possible, so that a data writing operation is also performed. be able to. As a result, the structure of the pickup head that can be used for both reading and writing data can be greatly simplified.
[0032]
In the above-described example, the multi-quantum well adjacent layer 104 includes three pairs of well layers and barrier layers. However, the number of pairs can be determined as appropriate depending on the layer thickness and the In composition. Further, the barrier layer is not limited to GaN, and may be a material containing In, Al, or the like.
[0033]
Next, a second embodiment of the present invention will be described.
FIG. 7 is a cross-sectional view illustrating a schematic configuration of a nitride-based semiconductor laser according to the second embodiment of the present invention. In the figure, 200 is a p-type SiC substrate, 201 is a p-type AlN buffer layer (Mg-doped, 3-5 × 10²⁰cm^-3, 0.1 μm), 202 is a p-type GaN layer (Mg-doped, 1 × 10¹⁹cm^-34 μm), 203 is p-type Al_0.3 Ga_0.7 N clad layer (Mg dove, 5 × 10¹⁷cm^-3, 0.3 μm), 204 is Al_0.1 Ga_0.9 N adjacent layer (undoped, 0.1 μm), 205 is a multiple quantum well active layer In_0.1 Ga_0.9 N / Al_0.1 Ga_0.9 N (undoped, well width 1 nm, barrier width 2 nm, number of pairs 3), 206 is Al_0.1 Ga_0.9 N adjacent layer (undoped, 0.1 μm), 207 is n-type Al_0.3 Ga_0.7 N clad layer (Si doped, 5 × 10¹⁷cm^-3, 0.3 μm), 208 is a p-type GaN current confinement layer (Mg-doped, 5 × 10¹⁷cm^-3, 0.1 μm), 209 is an n-type GaN contact layer (Si-doped, 1-3 × 10¹⁹cm^-30.1 μm), 210 is an n-side electrode, and 211 is a p-side electrode.
[0034]
The manufacturing method of this nitride semiconductor laser is as follows. First, a p-type GaN current confinement layer 208 is grown by MOCVD, and then a mask (not shown) is partially formed on the p-type GaN current confinement layer 208 by photolithography._0.3 Ga_0.7 Etching is performed until the N clad layer 207 is exposed. Next, the p-type GaN contact layer 209 is grown. Electrodes are formed on both sides, and then the cavity facets are formed by cleavage.
[0035]
In this embodiment, In_0.1 Ga_0.9 N / Al_0.1 Ga_0.9 The N multiple quantum well active layer 205 is also manufactured by the same process as the multiple quantum well adjacent layer 104 of the above-described embodiment. Specifically, TMG, TMI, and ammonia gas are used for the growth of InGaN, TMA (trimethylaluminum), TMG, and ammonia gas are used for the growth of the AlGaN layer, the growth temperature is 860 ° C., and the V / III ratio of the raw material About 170, and the growth interruption time in each layer is 1 second, and the growth is repeated three times. As a result, a multiple quantum well layer having a well thickness of 2 nm, a barrier thickness of 4 nm, and a pair number of 3 can be formed.
[0036]
By such a process, a region having a locally large indium (In) composition is also formed in the well layer portion of the multiple quantum well active layer 205. Specifically, in each well layer, a large number of island-like regions having a diameter of 2 nm and an In composition of about 20% are distributed in the plane. In this region, since there is more In than in the periphery, the lattice constant is shifted and distortion is applied. As a result, although the In content is large, the band gap is only 10 meV or less different from the surrounding region. When current is injected into this semiconductor laser, light emission is efficiently performed in this island-shaped region having a high In composition because the dopant Si is low and the conductivity is low.
[0037]
FIG. 8 is a schematic diagram showing a result of observing the active layer 205 with a transmission electron microscope. That is, in the active layer 205, island-like regions whose In concentration is higher than that of the periphery are regularly arranged in the in-plane direction. The diameter of the indium high-concentration composition region was approximately 70 nm, and the interval was approximately 200 nm. Further, as a result of experiments by the inventors, it has been found that the interval between the island regions can be controlled by changing the growth conditions.
[0038]
When the interval between the island regions is d and the refractive index of the periphery of the island regions is n, if the emission wavelength of the high concentration region is λ, then d = λm / 2n (m = 1, 2, 3 In the case of 4), the self-excited oscillation was able to occur most stably. When m exceeds 4, the stability of self-oscillation is reduced. This is usually considered to be due to selection of a large number of oscillation modes.
[0039]
According to the present embodiment, self-excited oscillation can be performed without using a complicated structure such as a distributed feedback laser, mode hopping can be suppressed, and low noise can be realized. I understood.
[0040]
FIG. 9 is a graph showing optimum growth conditions in each of the emission wavelengths of 400 to 430 nm. In other words, the horizontal axis in the figure is the growth temperature (° C.), and the vertical axis is the In content ratio (%), and the respective In content ratio in the solid layer and the optimum conditions for the growth temperature are shown for each emission wavelength. Show.
[0041]
There are few donors in the island-like indium high concentration region formed in the active layer. Therefore, the island-shaped region has high emission efficiency, and further promotes the stable existence of excitonic molecules (dipoles) with high emission efficiency due to the quantum confinement effect. As a result, the island-like region having a high In concentration is very small in volume, but an inversion distribution sufficient for laser oscillation can be formed. On the other hand, in the low In region around the region where the In concentration is high, the band gap is larger than that of the island region, but there are donors. Become. This state persisted even at high output.
[0042]
As for impurities doped in the active layer, the threshold value increased except for n-type Si, C, Ge, Sn, and Pb, which was not practical. On the other hand, in the case of Si, particularly high luminous efficiency was obtained.
[0043]
In the semiconductor laser of this structure, an oscillation wavelength of 375 nm was obtained at a threshold value of 10 mA, a fundamental transverse mode oscillation was observed, and stable operation up to 5000 hours was confirmed. In the present embodiment, SiC is used as the substrate, but any conductive substrate may be used. In the case of a ZnO substrate, further excellent current-voltage characteristics are obtained. The current confinement layer 208 may be provided on the substrate 200 side with respect to the active layer 205 or may be provided on both sides of the active layer 205. The material of the current confinement layer may be a material having a higher refractive index than that of the contact layer.
[0044]
Next, a third embodiment of the present invention will be described.
FIG. 10 is a sectional view of a nitride semiconductor laser showing the third embodiment of the present invention. In the figure, 300 is a sapphire substrate, 301 is a GaN buffer layer (0.01 μm), and 302 is a p-type GaN contact layer (Mg-doped, 3 to 5 × 10¹⁸cm^-31 μm), 303 is p-type Al_0.2 Ga_0.8 N clad layer (Mg doped, 5 × 10¹⁷cm^-3, 0.3 μm), 304 is a p-type GaN adjacent layer (Mg-doped, 5 × 10¹⁷cm^-3, 0.1 μm), 305 is In_0.3 Ga_0.7 N / GaN multiple quantum well active layer (undoped, well width 2 nm, barrier width 4 nm, number of pairs 3), 306 is an n-type GaN adjacent layer (Si doped, 5 × 10¹⁷cm^-3, 0.1 μm), 307 is n-type Al_0.2 Ga_0.8 N clad layer (Si doped, 5 × 10¹⁷cm^-3, 0.3 μm), 308 is a p-type GaN conduction barrier layer (Mg doped, 1 × 10¹⁸cm^-3, 0.3 μm) and 309 are n-type GaN contact layers (Si-doped, 1 to 3 × 10¹⁸cm^-30.5 μm), 310 is an n-side electrode, and 311 is a p-side electrode.
[0045]
The outline of the manufacturing method is described below. Crystal growth was performed by the MOCVD method. First, a GaN buffer layer 301 is grown on a sapphire substrate 300 by MOCVD. As shown in FIGS. 11A and 11B, a sapphire substrate 300 having a slit 320 is used. It was. Here, the opening of the cut 320 can be, for example, about 250 μm × 30 μm, and the interval between the cuts can be about 250 μm.
[0046]
In the present embodiment, first, the GaN buffer layer 301 is grown on the sapphire substrate 300 under the condition that the lateral growth rate is increased. That is, at the time of crystal growth, the growth of the GaN atoms on the substrate surface is increased by making the growth temperature sufficiently higher than the supply rate of GaN. By growing the buffer layer 301 under such conditions, the cut 320 of the sapphire substrate 300 is blocked by the GaN buffer layer 301.
[0047]
Thereafter, growth is sequentially performed from the p-type GaN contact layer 302 to the p-type GaN conduction barrier layer 308 in a normal growth state. After the growth up to the p-type GaN conduction barrier layer 308, a mask (not shown) is partially formed on the p-type GaN conduction barrier layer 308 by photolithography to form an n-type Al._0.2 Ga_0.8 Etching is performed until the N clad layer 307 is exposed. Next, the mask is removed, and an n-type GaN contact layer 309 is grown. Ni and Au are vapor-deposited on the contact layer 309 to form the n-side electrode 310. Further, the GaN buffer layer 301 is removed from the lower surface side of the substrate 300 by etching, and Pt, Ti, and Au are sequentially deposited to form the p-side electrode 311. In order to use this as a laser element, an end face (not shown) is formed by cleavage, and the semiconductor light emitting element is separated by dicing to obtain the semiconductor laser of FIG. Although not shown in the drawings, the end face is coated with a highly reflective coating made of a dielectric multilayer film.
[0048]
Next, the In in the present embodiment_0.2 Ga_0.8 Specific growth conditions for the N / GaN multiple quantum well active layer 305 will be described. The growth temperature is 740 ° C., the InGaN layer uses TMG, TMI, and ammonia gas, and the GaN layer uses TMG and ammonia gas. InGaN well layer has a growth rate of In_0.2 Ga_0.8 The GaN barrier layer grows for 20 seconds while stopping TMI under the growth condition of 1 μm / h obtained by N thick film growth. Further, a waiting time of 1.5 seconds is provided between the growth of the InGaN well layer and the GaN barrier layer. The growth rate differs between the thick film and the thin film such as the quantum well even if the growth conditions are the same, because the growth rate is different in the initial stage of growth. By performing such growth, In_0.2 Ga_0.8 In the N / GaN multiple quantum well active layer 305, a portion having a locally large In composition is formed in the well layer portion. Specifically, a large number of regions having a diameter of 2 nm and an In composition of about 30% are formed in each well layer. This region is distorted due to a large amount of In as compared with the surrounding area. This causes a large amount of In, but the band gap is only 10 meV or less different from the surrounding region. When current injection is performed on this nitride-based semiconductor laser, in this region where the In composition is high, the dopant Si is small, the conductivity is low, and carriers are injected mainly in the vicinity thereof.
[0049]
FIG. 12 is a schematic diagram showing a result of observation of the active layer 305 with a transmission electron microscope. That is, as a result of observing the lattice image with an electron microscope, it was observed that island layers having a diameter of several nm were scattered in the active layer 305. As a result of examining the composition of this island-shaped region using the characteristic X-ray spectrum analysis method, it was confirmed that the In concentration was higher than the surroundings. Furthermore, as a result of observation by the cathodoluminescence method, emission points regularly arranged corresponding to the island-like regions were observed.
[0050]
The reason why such island-shaped regions are formed is thought to be because island-shaped growth occurs in order to grow InGaN that does not lattice match with GaN on GaN. Here, the present inventor examined the relationship between the diameter of the island-like region formed under various growth conditions and the external quantum efficiency of the semiconductor laser.
[0051]
FIG. 13 is a graph showing the relationship between the size of the island region and the external quantum efficiency. That is, in the figure, the vertical axis represents the external quantum efficiency, and the horizontal axis represents the average diameter of the island regions. As can be seen from the figure, the external quantum efficiency tends to increase as the diameter of the island region decreases. In order to obtain a particularly high external quantum efficiency, it is desirable that the diameter of the island-shaped region is 100 nm or less. It has been found that when the diameter of the island-shaped region is further increased, the luminous efficiency is remarkably lowered as shown in FIG.
[0052]
Next, as a result of examining in detail the two-dimensional distribution of the indium concentration in the island region and its peripheral part, the present inventor found that the island region has a diameter of 100 nm or less. It was found that the indium concentration needs to change at a rate of 10% or more every 2 nm. That is, it has been found that an island-shaped region having a diameter of 100 nm or less can exist when there is a further sharp increase in indium concentration at the end of the island-shaped region.
[0053]
Since the high In composition portion in the active layer has few donors, the portion with a high In composition has good light emission efficiency. In addition, the quantum confinement effect promotes the stable existence of excitonic molecules with good emission efficiency. Thereby, the island-like high In region can form a population inversion sufficient to oscillate although it is minute in volume. The low In region around the island-like high-concentration region has a band gap larger than that of the island-like high-concentration region, but because of the presence of donors, it acts as a saturable absorption layer and becomes a self-excited oscillation state. . This state persisted even at high output.
[0054]
As impurities to be doped into the active layer, the threshold value increased except for n-type Si, C, Ge, Sn, and Pb, which was not practical.
In this embodiment, since the laterally grown GaN buffer layer 301 is provided under the active layer, there are extremely few dislocations and defects. As a result, the leakage current is suppressed, and the semiconductor light emitting device is hardly broken.
[0055]
The semiconductor laser of this embodiment oscillated continuously at room temperature with a threshold of 20 mA, the oscillation wavelength was 420 nm, and the operating voltage was 3.8V. Further, the S / N at the time of 50 mW operation is significantly improved to 130 dB as compared with 20 dB of the conventional semiconductor laser not using this structure by performing self-excited oscillation. Further, since a quantum well structure is employed for the active layer, a high output of 200 mW was obtained by self-excited oscillation, and 300 mW was obtained when the self-excited oscillation was not maintained. In addition, the lifetime of the semiconductor light emitting device is expected to be 100,000 hours or more due to the deterioration tendency in the life test, and low noise, high output, and high reliability can be realized.
[0056]
In this embodiment, a sapphire substrate is used as the substrate, or quartz glass, diamond, BN, or the like may be used. Further, when an MBE (Molecular Beam Epitaxy) method is used as a growth method, Pyrex glass, ZnO, or the like can also be used as a substrate.
[0057]
Next, a fourth embodiment of the present invention will be described.
FIG. 14 is for explaining a schematic configuration of a nitride-based semiconductor light emitting diode (LED) according to the fourth embodiment of the present invention. In this figure, 400 is a sapphire substrate, 401 is a GaN buffer layer (3-5 × 10¹⁸cm^-3, 4 μm), 402 is an n-type GaN contact layer (Si-doped, 1 × 10¹⁸cm^-3, 2 μm), 403 is an n-type GaN layer (Si-doped, 5 × 10¹⁷cm^-3, 0.1 μm), 404 is In_0.3 Ga_0.7 N / GaN 3MQW active layer (Si-doped, well layer 2 nm, barrier layer 4 nm), 405 is a p-type GaN layer (Mg-doped, 5 × 10¹⁷cm^-3, 0.1 μm), 406 is a GaN contact layer (Mg-doped, 3 × 10¹⁸cm^-30.05 μm), 410 is a p-side electrode, 411 is an n-side electrode, and 412 is an ITO (Indium Tin Oxide) transparent electrode.
[0058]
Each semiconductor layer in the figure was grown by MOCVD. During the growth of the active layer 404, each In_0.3 Ga_0.7 After the growth of the N well layer, an island-like region having a high In concentration was created by providing a growth interruption time of 1 to 3 seconds. Growth other than the active layer was performed by the usual growth method. After the growth, the portion that becomes the p-electrode is masked and dry-etched until the n-type GaN contact layer 402 is exposed to form a mesa shape. The mask is removed, and there is no SiO₂ Was attached. A transparent semiconductor electrode was formed on the top surface of the mesa shape, and a p-side electrode 410 was formed in a part far from the n-side electrode 411, and an n-side electrode 411 was formed, thereby obtaining a semiconductor light emitting device structure.
After the fabrication, the light emitting device was disassembled and the active layer portion was observed with a transmission electron microscope. As a result, a region where In was higher than the surrounding area was observed in the well layer portion, and the region was approximately 4 nm in diameter. Further, when examined by characteristic X-rays, it was found that this high concentration region contained about 10% more In concentration than the surrounding region with low In concentration.
The operating voltage of the device was 2.7 V, and the optical output was 10 mW at 10 mA. In addition, it was 50 mW at 100 mA. Luminous efficiency was good and the external quantum efficiency reached 30%. Such a high-efficiency device with high emission intensity was realized because carriers injected into the high In concentration region in the active layer were confined in the high In concentration region and non-radiative recombination occurred. This is because of recombination.
In this embodiment, only blue is used as the light source. However, by increasing the amount of In in the active layer, it is possible to emit light up to a wavelength close to red light, and if filters are used, the three primary colors of red, green, and blue can be obtained. A GaN-based full-color light emitting device can also be realized.
[0059]
Next, a fifth embodiment of the present invention will be described.
FIG. 15 is a view for explaining a schematic configuration of a nitride-based semiconductor light-emitting device according to the fifth embodiment of the present invention. In the light emitting device shown in the figure, on the sapphire substrate 500, a buffer layer 501, an n-type GaN contact layer (Si-doped, 3 to 5 × 10¹⁸cm^-34 μm) 502, n-type AlGaN cladding layer (Si doped, 5 × 10¹⁷cm^-3, 0.3 μm) 503, non-doped GaN adjacent layer (0.1 μm) 504, InGaN multiple quantum well (MQW) active layer 505, non-doped GaN adjacent layer (0.1 μm) 506, p-type AlGaN cladding layer (Mg-doped, 5 × 10¹⁷cm^-3, 0.3 μm) 507, p-type GaN contact layer (Mg-doped, 5 × 10¹⁸cm^-3, 0.5 μm) 508, SiO₂ A (silicon dioxide) film 509 is sequentially stacked. Reference numeral 510 denotes a p-side electrode, and 511 denotes an n-side electrode.
[0060]
The manufacturing method is as follows. A buffer layer 501 is grown on the substrate 500 by MOCVD, and then an n-type GaN contact layer 502 is formed using TMG (trimethylgallium), TMA (trimethylaluminum), ammonia, hydrogen, and nitrogen at a growth temperature of 1100 ° C. An n-type AlGaN cladding layer 503 and a non-doped GaN adjacent layer 504 are sequentially stacked.
[0061]
Next, the supply of the group III source gas is stopped, and the substrate temperature is lowered to 760 ° C. At this temperature, TMG was kept at -15 ° C., hydrogen gas was used as a carrier gas, 10 cc / min, ammonia at 10 ° C./min at 20 ° C., and nitrogen at 19.7 L / min. In addition, TMI (trimethylindium) was added. The InGaN multiple quantum well active layer 505 is grown by repeatedly switching and supplying 20 times at 1.5 ° C. in combination of 500 cc / min and 15 cc / min with nitrogen as a carrier gas at 37 ° C.
[0062]
Thereafter, the growth was stopped by stopping the supply of TMG and TMI, and the temperature was increased to 1100 ° C. over 4 minutes while flowing hydrogen at 40 cc / min, nitrogen at 19.96 L / min, and ammonia at 10 L / min. Warm up. Subsequently, the temperature is maintained at 1100 ° C., and hydrogen is supplied at 500 cc / min, nitrogen is supplied at 14.5 L / min, TMG is supplied at 100 cc / min, and ammonia is supplied at 10 L / min to stack the non-doped GaN adjacent layer 506. After this, Cp₂ Mg (biscyclopentadienyl magnesium) and TMA are added to form a p-type AlGaN cladding layer 507, and then the supply of TMA is stopped to form a p-type GaN contact layer 508. After this, SiO₂ The nitride-based semiconductor light-emitting device shown in FIG. 15 is completed through steps such as deposition of film 509, photolithography, etching, vapor deposition of p-side electrode 510 and n-side electrode 511, and alloy.
[0063]
In the above-described process, the growth temperature is increased to 760 ° C. after the adjacent layer 504 is grown, but this temperature is preferably 700 ° C. or higher and 850 ° C. or lower. The reason for this will be described below.
[0064]
In order to investigate the growth conditions of InGaN, the inventor first sets the total flow rate of the source gas and the carrier gas to 30 liters per minute, sets the gas flow rate ratio of the group V element to the group III element to 8400, InGaN was grown at various growth temperatures. When this was evaluated by photoluminescence (Photo Luminescence: PL), as shown in Table 1, PL light having a sufficient intensity could be observed in the range of 700 ° C. to 850 ° C. When the growth temperature is lower than 700 ° C., the growth becomes insufficient and the PL emission intensity does not increase. When the growth temperature exceeded 850 ° C., the crystal was damaged, so that the PL emission intensity was extremely reduced.
[0065]
[Table 1]

[0066]
Next, the inventor fixed the growth temperature at 760 ° C., set the sum of the flow rates of the source gas and the carrier gas to 30 liters per minute, and investigated the dependence of the group V element and the group III element on the molar flow rate ratio. . As a result, as shown in Table 2, when the molar flow ratio of the group V element to the group III element was 1000 or more and 15000 or less, PL light emission with sufficient intensity was observed.
When the molar flow rate ratio of the group V element and the group III element is less than 1000, the PL emission intensity does not increase because the reaction does not sufficiently occur.
If the molar flow ratio of the group V element to the group III element exceeds 15000, the group V element is interrupted and reacts with the crystal lattice to which the group III element should react, and the group III element cannot sufficiently react. The PL emission intensity was extremely reduced.
[0067]
[Table 2]

[0068]
Furthermore, the growth temperature was fixed at 760 ° C., the flow rate ratio of the Group V element to the Group III element was 8400, and the dependence on the total flow rate per minute of all the source gases and the carrier gas was examined. Thus, when the total flow rate per minute was 10 liters or more and 50 liters or less, sufficient PL emission was observed. When the total flow rate per minute is less than 10 liters, the PL emission intensity does not increase because the reaction does not sufficiently occur. When the total flow rate per minute exceeded 50 liters, the flow rate increased and sufficient reaction time could not be obtained, so that the PL emission intensity was extremely reduced.
[0069]
[Table 3]

[0070]
In this embodiment, neither the InGaN multiple quantum well active layer 505 nor the non-doped GaN adjacent layer 506 is intentionally doped. According to experiments by the present inventors, it has been found that when grown as described above, the GaN layer has a higher resistance than the InGaN layer. Further, when a cross section of the grown layer was observed with a TEM (transmission electron microscope), a hole-like region (pit) was present in the InGaN multiple quantum well active layer 505, and this pit was buried by the non-doped GaN adjacent layer 506. It was found that it was flattened. Therefore, according to the semiconductor light emitting device of the above-described embodiment, self-excited oscillation occurs according to the principle described below.
[0071]
That is, due to the presence of the hole-shaped region in the active layer, the current flowing in the active layer is distributed, and the low current density region becomes the saturable absorption region, so that self-excited oscillation occurs. This will be described in detail below.
[0072]
FIG. 16 is a schematic cross-sectional view showing the flow of injected current in the light emitting device of this embodiment. In the figure, for the sake of easy understanding, a simplified structure of the light emitting element shown in FIG. 16 will be described as an example. As shown in FIG. 16, there is a heterojunction between the non-doped GaN layer 553 and the non-doped InGaN layer 554, and there is a hole (pit) P at the interface on the non-doped InGaN layer 554 side. A p-side electrode 551 and an n-side electrode 556 are connected to both via a p-type contact layer 552 and an n-type contact layer 555, respectively.
[0073]
Assuming that a voltage is applied to both electrodes in the forward direction, the non-doped GaN layer 553 has a larger band gap than the non-doped InGaN layer 554, so that the current flows as indicated by the arrows in FIG. The current density in the portion below the hole-shaped region of 554 is sparse compared to the current density in other regions.
[0074]
In order to verify this phenomenon, the present inventor performed a two-dimensional simulation and examined the current distribution. FIG. 17 shows the layer structure used in the simulation. The layer structure mimics the laser structure and is 5 × 10¹⁸cm^-3Doped n-type GaN contact layer 561, 5 × 10¹⁷cm^-3Doped n-type Al with a thickness of 0.3 μm_0.15Ga_0.85N-cladding layer 562, non-doped GaN adjacent layer 563 with a thickness of 0.1 μm, non-doped In with a thickness of 0.1 μm_0.08Ga_0.92N active layer 564, 0.1 μm thick non-doped GaN adjacent layer 565, 5 × 10¹⁷cm^-3Doped p-type Al with a thickness of 0.3 μm_0.15Ga_0.85N clad layer 566, 5 × 10¹⁸cm^-3And a p-type GaN contact layer 567 having a thickness of 0.1 μm. Non-doped In_0.08Ga_0.92Hole-like regions (pits) P having a width of 0.1 μm and a depth of 0.05 μm are arranged at an interval of 1 μm at the interface of the N active layer 564 in contact with the non-doped GaN adjacent layer 563. Although the actual pit shape is not necessarily such a rectangle, a simulation was performed with such a shape for the sake of simplicity of calculation. Needless to say, the difference in shape does not have a substantial effect on the simulation results.
[0075]
FIG. 18 shows the distribution of current density immediately below the hole-like region (pit) when a voltage of 4 V is applied to such a structure. The current density is reduced by 30% or more in the pit portion. Thus, it has become clear that the current density is brought about by the presence of the hole-like region. Then, such a current distribution is generated, and when laser oscillation occurs, first, oscillation starts at a portion where the current is dense, and a portion where the current is sparse becomes a saturable absorber. Note that the adjacent layer is not non-doped and is 5 × 10 5.¹⁷cm^-3The same result was obtained when the material was doped. As described above, the presence of the hole-shaped region causes current density. The portion where the current is sparse becomes a saturable absorber, and self-oscillation can be realized.
[0078]
  Next, the first of the present invention6The embodiment will be described. Figure19Is the first of the present invention6This is for explaining a schematic configuration of the nitride-based semiconductor light-emitting device according to the embodiment. In the figure, 700 is a sapphire substrate, 701 is a buffer layer, 702 is an n-type GaN contact layer (Si-doped, 3 to 5 × 10¹⁸cm^-34 μm) and 703 are n-type AlGaN cladding layers (Si-doped, 5 × 10¹⁷cm^-3, 0.3 μm), 704 is n-type In_0.1 Ga_0.9 N / In_0.02Ga_0.98N multiple quantum well adjacent layer (Si doped, 5 × 10¹⁷cm^-3, Well width 2 nm, barrier width 4 nm, 20 layers), 705 is In_0.2 Ga_0.8 N / In_0.05Ga_0.95N multiple quantum well active layer (non-doped, well width 2 nm, barrier width 4 nm, 10 layers), 706 is a p-type GaN adjacent layer (Mg-doped, 5 × 10¹⁷cm^-3, 0.1 μm), 707 is a p-type AlGaN cladding layer (Mg-doped, 5 × 10¹⁷cm^-3, 0.3 μm) and 708 are p-type GaN contact layers (Mg-doped, 5 × 10¹⁸cm^-3, 0.5 μm), 709 is SiO₂ A film, 710 is a p-side electrode, and 711 is an n-side electrode.
[0079]
n-type In_0.1 Ga_0.9 N / In_0.02Ga_0.98The N multiple quantum well adjacent layer 704 is grown as follows. Growth temperature is 760 ° C, In_0.1 Ga_0.9 For growth of N well layer, TMI, TMG, ammonia, SiH_Four Then, a well layer having a thickness of 2 nm is grown. Next, after waiting for 1 second with only ammonia supplied, TMI, TMG, ammonia, SiH_Four 4 nm thick In_0.02Ga_0.98N barrier layer is grown. Next, a well layer is grown in the same manner with a waiting time of 1 second again. By repeating such a process 20 times in total, n-type In_0.1 Ga_0.9 N / In_0.02Ga_0.98An N multiple quantum well adjacent layer 704 can be formed.
[0080]
Also, In_0.2 Ga_0.8 N / In_0.05Ga_0.95The growth method of the N multiple quantum well active layer 705 is as follows. At a growth temperature of 760 ° C, In_0.2 Ga_0.8 N is grown by 2 nm, and a 1 second standby time is set._0.05Ga_0.95Grow N. This cycle is repeated a total of 10 times.
[0081]
By such a growth method, n-type In_0.1 Ga_0.9 N / In_0.02Ga_0.98N multiple quantum well adjacent layer 704 and In_0.2 Ga_0.8 N / In_0.05Ga_0.95Both the N multiple quantum well active layer 705 can have a structure having island-like regions and pits.
[0082]
  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, from the first to the first mentioned above6In this embodiment, the active layer is a non-doped layer, but may be doped n-type or p-type. Further, the adjacent layer may not be doped, or may be doped n-type or p-type. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.
[0083]
【The invention's effect】
As described above in detail, according to the nitride-based semiconductor laser of the present invention, a nitride-based semiconductor light-emitting element that generates self-excited oscillation can be obtained with a high probability without using a complicated structure. As a result, a semiconductor laser satisfying the practical performance as a semiconductor laser for reading optical disc recording with low noise characteristics can be easily produced at low cost, and its usefulness is tremendous. Furthermore, reading and writing from the recording medium can be performed by the nitride semiconductor laser having the same structure, and the structure of the read / write combined head can be greatly simplified.
On the other hand, according to the nitride semiconductor light emitting diode of the present invention, a nitride light emitting diode with high luminous efficiency was obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first embodiment of a nitride-based semiconductor light-emitting device according to the present invention.
2 is a schematic diagram showing an in-plane light emission distribution of the multiple quantum well adjacent layer 104 shown in FIG.
3 is a graph showing the relationship between the In composition ratio and the donor concentration in the multiple quantum well adjacent layer 104 shown in FIG.
4 is a schematic diagram showing a band structure in the multiple quantum well adjacent layer 104 shown in FIG. 1. FIG.
5 is a graph showing the rate of occurrence of self-oscillation with respect to the light output of the nitride-based semiconductor light-emitting device shown in FIG.
FIG. 6 is a schematic diagram for explaining a state in which a semiconductor laser is applied to reading of an optical disc.
FIG. 7 is a cross-sectional view showing a second embodiment of the nitride-based semiconductor light-emitting device of the present invention.
FIG. 8 is a schematic diagram showing a result of observing the active layer 205 shown in FIG. 7 with a transmission electron microscope.
9 is a graph showing manufacturing conditions for the nitride-based semiconductor light-emitting device shown in FIG.
FIG. 10 is a cross-sectional view showing a third embodiment of the nitride-based semiconductor light-emitting device of the present invention.
11 is a schematic view showing the structure of a substrate used in the nitride-based semiconductor light-emitting device shown in FIG. 10, wherein (a) is a plan view and (b) is a side view.
12 is a schematic diagram showing a result of observation of an active layer 305 shown in FIG. 10 with a transmission electron microscope.
13 is a graph showing the relationship between the average diameter of island regions in the active layer 305 shown in FIG. 10 and the external quantum efficiency of the semiconductor light emitting device.
FIG. 14 is a cross-sectional view showing a fourth embodiment of the nitride-based semiconductor light-emitting device of the present invention.
FIG. 15 is a cross-sectional view showing a fifth embodiment of the nitride-based semiconductor light-emitting element of the present invention.
FIG. 16 is a schematic diagram showing a current path when an adjacent layer has a band gap larger than that of an active layer.
FIG. 17 is a schematic diagram showing a layer structure used in a two-dimensional simulation.
18 is a distribution diagram of current density immediately below a hole-shaped region when a voltage of 4 V is applied in a two-dimensional simulation for the element shown in FIG.
[Figure19The nitride-based semiconductor light-emitting device of the present invention6It is sectional drawing which shows this embodiment.
[Explanation of symbols]
100 sapphire substrate,
101 n-type GaN buffer layer
102 n-type GaN contact layer
103 n-type AlGaN cladding layer
104 n-type In_0.1 Ga_0.9 N / GaN multiple quantum well adjacent layer
105 In_0.3 Ga_0.7 N / GaN multiple quantum well active layer
106 P-type GaN adjacent layer
107 p-type AlGaN cladding layer
108 p-type GaN contact layer
109 n-type GaN conducting barrier layer
110 p-side electrode
111 n-side electrode
150 Laser light
152 lens
154A Nitride-based semiconductor laser beam according to the invention
154B Laser beam of conventional DVD system
154C Compact Disc System Laser Beam
160 Optical disc
162 tracks
164 pit
200 p-type SiC substrate
201 p-type AlN buffer layer
202 p-type GaN layer
203 p-type Al_0.3 Ga_0.7 N clad layer
204 Al_0.1 Ga_0.9 N adjacent layer
205 In_0.1 Ga_0.9 N / Al_0.1 Ga_0.9 N multiple quantum well active layer
206 Al_0.1 Ga_0.9 N adjacent layer
207 n-type Al_0.3 Ga_0.7 N clad layer
208 p-type GaN current confinement layer
209 n-type GaN contact layer
210 n-side electrode
211 p-side electrode
300 Sapphire substrate
301 GaN buffer layer
302 p-type GaN contact layer
303 p-type Al_0.2 Ga_0.8 N clad layer
304 p-type GaN adjacent layer
305 In_0.3 Ga_0.7 N / GaN multiple quantum well active layer
306 N-type GaN adjacent layer
307 n-type Al_0.2 Ga_0.8 N clad layer
308 p-type GaN conducting barrier layer
309 n-type GaN contact layer
310 n-side electrode
311 p-side electrode
400 Sapphire substrate
401 GaN buffer layer
402 n-type GaN contact layer
403 n-type GaN layer
404 In_0.3 Ga_0.7 N / GaN 3MQW active layer
405 p-type GaN layer
406 p-type GaN contact layer
410 p-side electrode
411 n-side electrode
412 ITO transparent electrode
500 Sapphire substrate
501 Buffer layer
502 n-type GaN contact layer
503 n-type AlGaN cladding layer
504 Non-doped GaN adjacent layer
505 InGaN MQW active layer
506 Non-doped GaN adjacent layer
507 p-type AlGaN cladding layer
508 p-type GaN contact layer
509 SiO₂ film
510 p-side electrode
511 n-side electrode
551 p-side electrode
552 p-type contact layer
553 Non-doped GaN layer
554 Non-doped InGaN layer
555 n-type contact layer
556 n-side electrode
P pit
561 n-type GaN contact layer
562 n-type Al_0.15Ga_0.85N clad layer
563 Non-doped GaN adjacent layer
564 Non-doped In_0.08Ga_0.92N active layer
565 Non-doped GaN adjacent layer
566 p-type Al_0.15Ga_0.85N clad layer
567 p-type GaN contactlayer
700    Sapphire substrate
701 Buffer layer
702 n-type GaN contact layer
703 n-type AlGaN cladding layer
704 n-type In_0.1 Ga_0.9 N / In_0.02Ga_0.98N multiple quantum well active layer
705 In_0.2 Ga_0.8 N / In_0.05Ga_0.95N multiple quantum well active layer
706 p-type GaN adjacent layer
707 p-type AlGaN cladding layer
708 p-type GaN contact layer
709 SiO₂ film
710 p-side electrode
711 n-side electrode

Claims (9)

  In a nitride semiconductor light emitting device in which a mixed crystal layer made of a ternary or higher III-V compound semiconductor having a hexagonal crystal structure is formed on a substrate, including an active layer and an adjacent layer adjacent thereto The adjacent layer has a multiple quantum well structure containing InGaN, and the adjacent layer is dotted with island-like regions having a higher concentration of indium constituting the adjacent layer than the surroundings. A nitride-based semiconductor light-emitting device having a maximum diameter of 100 nm or less and an impurity concentration in the island-shaped region being lower than that in a peripheral portion.   The nitride-based semiconductor light-emitting device according to claim 1, wherein the active layer is dotted with hole-like regions, and the hole-like regions are filled with a semiconductor forming the adjacent layer.   The nitride-based semiconductor light-emitting element according to claim 1, wherein the adjacent layers are dotted with hole-shaped regions.   The active layer has a multiple quantum well structure, and this active layer is dotted with island-like regions where the concentration of indium constituting the active layer is higher than that of the periphery. The nitride-based semiconductor light-emitting element according to claim 1, wherein the nitride-based semiconductor light-emitting element has a band gap that is the same as or smaller than a band gap of a material in the surrounding region.   5. The nitride semiconductor light emitting device according to claim 1, wherein the impurity is at least one of Si, C, Ge, Sn, and Pb.   When the distance between the island regions is d, the refractive index of the periphery thereof is n, and the emission wavelength of the island regions is λ, λm = 2nd (m = 1, 2, 3, 4) is satisfied. The nitride-based semiconductor light-emitting device according to claim 4.   The active layer is dotted with hole-like regions, the hole-like regions are embedded with a semiconductor forming the adjacent layer, and the adjacent layer is dotted with hole-like regions. 7. The nitride-based semiconductor light-emitting element according to claim 4, wherein the nitride-based semiconductor light-emitting element is embedded with a semiconductor that forms a layer adjacent to the adjacent layer but not on the active layer side.   Nitride-based semiconductor light-emitting device in which a mixed crystal layer composed of a ternary or higher group III-V compound semiconductor having a hexagonal crystal structure is formed on a substrate, including an active layer and an adjacent multiple quantum well layer In the device manufacturing method, the multiple quantum well adjacent layer has a multiple quantum well structure containing InGaN, and a source gas for growing the well layer and a source gas for growing the barrier layer are alternately supplied for a predetermined time. The well layer and the barrier layer are alternately grown, and a predetermined waiting time is provided between the growth of the well layer and the growth of the barrier layer. A nitride-based semiconductor light-emitting device in which island-shaped regions having a maximum diameter of 100 nm or less and a maximum diameter lower than that of the periphery and having an impurity concentration lower than that of the periphery are dotted. of Production method. 9. The nitride according to claim 8 , wherein the source gas for growing the well layer is trimethylindium, trimethylgallium and ammonia gas, and the source gas for growing the barrier layer is trimethylgallium and ammonia gas. For manufacturing a semiconductor light emitting device.

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